Nanotechnological
Communication
Biosci. Biotech. Res. Comm. 9(3): 495-502 (2016)
Amino acid binding to nanotube: Simulation of
membrane protein channels by computational methods
N. A. Moghaddam
1
, Saharnaz Ahmadi
2
and Reza Rasoolzadeh*
3
1
Department of Biology, Central Tehran Branch, Islamic Azad University, Tehran, Iran
2
Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran
3
Young ResearchersandElites club, Science and Research Branch, Islamic Azad University, Tehran, Iran
ABSTRACT
The importance of ionic channels is due to the passage of ions across the cell membrane which is based on electro-
chemical gradients. The structure of ionic channels often includes one or several central cores which makes up the
pore. The direct electron transfer between the enzyme and unmodi ed electrode is usually prohibited due to shielding
of the redox active sites by the protein shells. Monte Carlo simulation have been used to investigate protein folding
pathways with some success. Monte Carlo was originally developed for calculating equilibrium properties of physi-
cal systems .In calculations we optimized the geometry and de ned Potential Energy of the nanotube structure by
performing molecular mechanics calculation using MM+ force  eld, if too large a time step is used in Monte Carlo
simulation, it is possible to have a basic instability in the equations that result in a molecule blowing apart, we need
small time steps to preserve integration accuracy, however in the Monte Carlo time step 50 femtoseconds (0.05ps)
was appropriate. next step we calculated the Vibrational modes of the tube by applying the semi-empirical molecu-
lar orbital method. In this paper, we have studies the stability of CNT-Amino acids clusters using by semi-empirical
method and investigation of vibrational frequencies and electrical properties. In the more the potential energy
increases the more the conductivity of nanochannels decreases and we chose the least energy among nanotube and
amino acid complexes. Also the more energy we use, the more conductivity we will have; therefore, we choose the
complex which conducts the most current.
KEY WORDS: AMINO ACIDS- CNT- MEMBRANES PROTEINS- MONTE CARLO- SEMI EMPIRICAL
495
ARTICLE INFORMATION:
*Corresponding Author: Reza.Rasoolzadeh@gmail.com
Received 11
th
Aug, 2016
Accepted after revision 20
th
Sep, 2016
BBRC Print ISSN: 0974-6455
Online ISSN: 2321-4007
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NAAS Journal Score 2015: 3.48 Cosmos IF : 4.006
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Online Contents Available at: http//www.bbrc.in/
496 STUDY OF AMINO ACIDS BINDING TO NANOTUBE BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS
Nastaran, Saharnaz and Reza
INTRODUCTION
Protein helices which make up the pore have consisted
of four distinct subunits or one subunit which includes
repetitive parts. Any disorder in protein-made channels
causes paroxysm attacks. For instance, we can mention
neuromuscular diseases as one type of these illnesses.
These diseases are called disorders of ionic canals.
The function of channels is to allow selectivity and
speci city for a Variety of molecular species transport
across the cell membrane (Hornig et al. 2013, Rui et al.
2012). These channels, included: a) ligand-gated chan-
nels, b) voltage-gated channels, c) Second messenger
gated channels, d) mechanosensitive channels, e) Gap
junctions: porins not gated (Mollaamin et al. 2010, Lac-
roix et al. 2014).
The  rst step in understanding the physical mech-
anism of potassium transport through this protein
nanopore is the determination of the water molecu-
lar distribution along the axial length of the pore Ion
channels which are membrane proteins that mediation
ux between the outside of the cell through a small,
water- lled hole in the membrane-a pore. Ion- Selec-
tive pores were originally proposed to explain separate
Components of Na
+
, K
+
and leak currents in the clas-
sic experiments of Hodgkin and Huxley (Chone 2002 ,
Lee. AG. 2004). Potassium channels are the most diverse
group of the ion channel family (Hornig et al. 2013). The
recent determination of the crystallographic structure a
bacterial K
+
channel from Streptomyces lividans (KcsA)
(Syeda et al. 2012) has provided the molecular basic
for understanding the physical mechanisms control-
ling ionic selectivity, permeation, and transport through
Various types of K
+
channels. (Mantegazza and Catterall
2012, Rui et al. 2012).
In all cases, the functional K
+
channel is tetramer
(Mollaamin et al. 2010), typically of four identical Subu-
nits folded around a central Port (Syeda et al. 2012).
Voltage – gated potassium (Kv) channels are members of
the voltage – gated ion channel superfamily (Hornig et
al. 2013, Syeda et al. 2012), which is important for inita-
tion and propagation of action potentials in excitable
cells. They are composed of four identical or homolo-
gous Subunits, each containing six transmembrane
segments: S1-S6. Segments: S1-S4 form the voltage-
sensing domain (VSD), and segments S5 and S6 Con-
nected by the P loop, which is involved in ion selectivity,
Comprise the pore- forming domain (PD) S4 has four
gating – charge- carrying arginines (R1-R4) spaced at
intervals of three amino acid residues, which are highly
conserved and are thought to play a key role in coupling
changes in membrane Voltage to opening and closing of
the pore (Mantegazza and Catterall 2012, Mollaamin et
al. 2010). In the K
v
channels 13 electronic charges across
the membrane electrical  eld per channel between the
closed and open states (Lacroix et al. 2014, Vladimir et
al. 2006). Arginine residues interacting with lipid phos-
phate groups play an important role in stabilizing the
voltage- Sensor domain of the KvAP channel within a
bilayer. Simulations of the bacterial potassium channel
kcsA reveal speci c interactions of phosphatidylglycerol
with an acidic lipid-binding site the interface between
adjacent protein monomers.
Molecular and langevin dynamics simulation as well
as Monte Carlo simulation have been used to investi-
gate protein folding pathways with some success. The
metropolis Monte Carlo was originally developed for
calculating equilibrium properties of physical systems
(Sonoda et al. 2011, Sansom et al.2005, Jafari-Dehkordi
et al. 2015).
The metropolis algorithm performs a sample of the
con guration space of system starting from a random
conformation and repeating a large number of steps.
Molecular dynamics simulation is one the most promis-
ing approaches for solving the protein folding problem
.in this method we observe the time behavior of atoms
of the system. In MD simulation, new positions of atoms
are calculated by numerical integration of newton’s
equation of motion (Mollaamin et al. 2011, Cooke and
Schiller 2008).
The repentance of the existence of buckminster-
fullerene CNT (Kroto et al. 1985), theoretical specula-
tion about carbon clusters (Mollaamin et al. 2011) over
36 years was  nally veri ed. Since then, this beautiful
molecule has attracted ever more attention of theoreti-
cal and experimental scientists. Some chemists began
to focus their research on the chemistry of this mole-
cule, but real fullerene chemistry began only after 1990.
described a method for preparing macroscopic quantities
of CNT (Oh et al. 2011).
Direct electron transfers between the electrode and
the redox enzyme is very important for fundamental
studies and construction of biosensors (Liang et al. 2010,
Albareda-Sirvent and Hart 2001). However, the direct
electron transfer between the enzyme and unmodi ed
electrode is usually prohibited due to shielding of the
redox active sites by the protein shells (Wang et al.2008,
Mollaamin et al. 2010).
Therefore, several studies have been made to enhance
the electron transfer. Mediators are widely used to access
the redox center of an enzyme and then to act as the
charge carriers. Mediators can minimize the effects of
interferences, lower the operating potential of the elec-
trodes, and improve the linear response range and sen-
sitivity of the sensor (Zhang et al. 2005). Use of carbon
nanotubes (CNTs) as mediators has attracted increasing
attention in recent years. Comparing with traditional
carbon electrodes, CNTs show unique properties, such as
BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS STUDY OF AMINO ACIDS BINDING TO NANOTUBE 497
Nastaran, Saharnaz and Reza
good conductivity, high chemical stability, and catalytic
activities towards many electrochemical reactions (Mol-
laamin et al. 2010, Wang et al. 2008, Liang et al. 2010,
Manso et al. 2007, Jurkschat et al. 2006). More impor-
tantly, it is possible to bring the nanotubes close to the
redox centers of the proteins (Gooding et al. 2003, Liu
et al. 2003).
MATERIAL AND METHODS
Many studies have shown that the carbon nanotubes pos-
sess remarkable mechanical and physical properties lead-
ing to many potential applications such as  uid trans-
port,  uid storage at nanoscale, and nanodevices for drug
delivery
Since controlled experiments at the nanometer
scale are very dif cult, the simulation techniques have
been widely and successfully used to investigate the
mechanical property, wave propagation and resonant fre-
quency (Natsukia et al. 2008).The vibration of molecules
is best described using a quantum mechanical approach.
A harmonic oscillator does not exactly describe molecular
vibrations. Bond stretching is better described by a Morse
potential and conformational changes have sine-wave-
type behavior. However, the harmonic oscillator descrip-
tion is very useful as an approximate treatment for low
vibrational quantum numbers (Youky et al. 2009
).
A harmonic oscillator approximation is most widely
used for computing molecular vibrational frequencies
because more accurate methods require very large amounts
of CPU time. Frequencies computed with the Hartree-
Fock approximation and a quantum harmonic oscillator
approximation tends to be 10% too high due to the har-
monic oscillator approximation and lack of electron cor-
relation (Fernandez et al. 2006). The high-frequency oscil-
lations encountered using  exible water models are of the
order of 3500 cm
-1
which are somewhat larger than the
CNT vibrational modes of 1500 cm
-1
(Walther et al. 2001).
Hence, for this case study, the use of the  exible water
and solvent model. Vibrational frequencies from semi-
empirical calculations tend to be qualitative in (which)
they reproduce the general trend mentioned in the Results
here. However, the actual values are erratic. Some values
will be close, whereas others are often too high. However,
PM3 is generally more accurate than AM1.
Since periodic boundary conditions cannot be
adopted,  rst principles calculations of  nite-length
SWCNTs are only affordable to relatively small systems
with C atom number less than 300 within our present
computational ability (Ma and Guo (2008).
The molecular mechanics method using the MM+
force  eld, and the Austin Model 1 (AM1) (Dewar et al.
1985) and Parameterized Model number 3 (PM3) (Stew-
art 1989) semi-empirical method within the Restricted
Hartree–Fock (RHF) formalism are suf cient to study
carbon systems (Erkoc 2004). In 1989, Stewart improved
the techniques of parameterization and published PM3,
which gave lower average errors than AM1, are suf -
cient to study carbon systems, mainly for the enthalpies
of formation (Stewart 1989).
Purpose of C60 is nanotube that includes 60 carbons.
All calculations presented here were performed with
semi-empirical Molecular mechanics (MM+) (Table 2).
In the  rst step of the calculations we optimized the
geometry and de ned Potential Energy of the nanotube
structure by performing molecular mechanics calcula-
tion using MM+ force  eld, if too large a time step is
used in Monte Carlo simulation, it is possible to have
a basic instability in the equations that result in a mol-
ecule blowing apart, we need small time steps to pre-
serve integration accuracy, however in the Monte Carlo
time step 50 femtoseconds (0.05ps) was appropriate (Sa
Najafabadi et al. 2015). In the next step we calculated
the
Vibrational modes of the tube by applying the semi-
empirical molecular orbital method by the Hyperchem-7
package program (Hyperchem 7.0 2007).
RESULTS AND DISCUSSION
The resulting method was denoted, and in a sense, it is the
best set of parameters (or at least a good local minimum)
for the given set of experimental data . The optimization
process, however, still requires some human intervention
in selecting the experimental data and assigning appro-
priate weight factors to each set of data. As a reference
Table1 is the result of semi-empirical computation using
both method AM1& PM3.At the  rst glance in Table1, it
can be observed by increasing dielectrics, normal modes
will move to upper normal modes ratio and Vibrational
frequencies resulted from semi-empirical Calculations
tend to be qualitative. Therefore, by increasing dielec-
tric the higher frequency will be gained in which semi-
empirical methods will have the same operating proce-
dure (Mollaamin and Monajjemi 2015).
The PM3 and AM1 methods are also more popular
than other semi-empirical methods due to the availabil-
ity of algorithms for including salvation effects in these
calculations. There are also some known strengths and
limitations of PM3. Overall heats of formation are more
accurate than with AM1. Hypervalent molecules are
also predicted more accurately. On average, PM3 pre-
dicts energies more accurately than AM1.The heats of
formation are more accurate than AM1 or PM3 depend-
ing on the nature of the system and information desired,
they will often give the most accurate obtainable results
for organic molecules with semi-empirical methods. On
average, PM3 predicts energies and geometries better
than AM1 (Christensen et al. 2016).
498 STUDY OF AMINO ACIDS BINDING TO NANOTUBE BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS
Nastaran, Saharnaz and Reza
Table1a: Calculated Properties of CNT and binding to amino acids. (A) Electric Potential, (B) Electrostatic Properties,
(C) Total atomic charges
CNT
(B)
CNT-Ala-Gly CNT-Val-Ala
Atomic
number
ABC
Atomic
number
ABC
Atomic
number
AB C
C
1
-14.562 5.91621 0.049 N
1
-18.293 6.77 -0.446 N
1
-18.28 6.52 -0.25
C
2
-14.562 5.91621 0.050 C
2
-14.653 7.79 -0.107 C
2
-14.65 7.76 0.02
C
5
-14.559 5.91623 0.053 C
3
-14.621 9.10 0.337 C
3
-14.64 8.55 0.33
C
6
-14.560 5.91621 0.051 O
4
-22.238 9.32 -0.285 O
4
-22.25 8.26 -0.33
C
9
-14.56 5.91624 0.052 C
5
-14.714 8.26 -0.413 C
5
-14.71 8.78 -0.12
C
10
-14.560 5.91625 0.052 C
14
-14.744 6.07 -0.207 C
6
-14.73 9.20 -0.42
C
51
-14.567 5.91618 0.068 C
56
-14.657 5.75 0.027 C
7
-14.74 10.07 -0.40
C
52
-14.568 5.91619 0.061 N
66
-18.404 9.75 -0.406 C
13
-14.69 5.52 -0.24
C
55
-14.592 5.91619 0.040 C
67
-14.735 8.57 -0.240 C
66
-14.73 6.28 -0.10
C
56
-14.588 5.91617 0.045 C
68
-14.690 7.36 0.358 N
68
-18.39 8.64 -0.63
C
59
-14.604 5.91634 0.022 O
69
-22.367 7.65 -0.429 C
69
-14.72 7.89 -0.11
C
60
-14.607 5.91634 0.025 C
70
-14.69 7.51 0.31
O
71
-22.35 7.89 -0.40
C
72
-14.77 8.95 -0.37
CNT- Ala-Leu CNT-Ser-Thr CNT-Gln-Asn
Atomic
Number
ABC
Atomic
number
ABC
Atomic
number
AB C
N1 -18.301 7.33 -0.393 N
1
-18.30 7.14 -0.50 N
1
-18.264 6.30 -0.469
C
2
-14.673 7.85 -0.188 C
2
-14.67 8.09 -0.10 C
2
-14.664 7.48 -0.047
C
3
-14.651 9.29 0.322 C
3
-14.64 8.44 0.36 C
3
-14.666 7.53 0.339
O
4
-22.260 9.85 -0.310 O
4
-22.23 7.99 -0.25 O
4
-22.257 6.68 -0.386
C
5
-14.765 7.20 -0.399 C
5
-14.67 9.46 -0.01 C
5
-14.728 8.71 -0.236
C
6
-14.683 7.85 0.135 O
6
-22.31 10.44 -0.59 C
6
-14.733 9.94 -0.351
C
60
-14.776 5.48 -0.172 C
8
-14.71 5.85 0.30 C
7
-14.733 11.19 0.513
N
66
-18.382 8.94 -0.368 C
61
-14.69 5.97 0.03 O
8
-22.361 11.23 -0.453
C
67
-14.714 7.86 -0.116 N
67
-18.42 8.89 -0.46 N
9
-18.329 12.34 -0.718
C
68
-14.729 6.50 0.3 62 N
68
-14.70 8.05 -0.12 C
15
-14.776 6.32 0.020
O
69
-22.364 6.59 -0.452 C
69
-14.68 6.94 0.04 C
69
-14.649 5.53 0.101
C
70
-14.743 8.23 -0.231 O
70
-22.30 6.94 -0.34 N
70
-18.412 9.61 -0.423
C
71
-14.735 7.38 -0.133 C
71
-14.64 7.63 -0.03 C
71
-14.726 8.39 -0.136
C
72
-14.771 7.57 -0.389 O
72
-22.17 6.91 -0.47 C
72
-14.714 7.20 0.175
C
73
-14.756 8.17 -0.395 C
73
-14.74 8.989 -0.38 O
73
-22.346 7.53 -0.320
C
74
-14.728 8.61 -0.344
C
75
-14.619 7.57 0.561
O
76
-22.335 6.55 -0.470
N
77
-18.309 8.02 -0.711
There is energy of interaction in between solvent and
solute. Therefore, the solute properties dependent on
energy, such as geometry, total energy and vibrational
frequencies depend on the solvent. The presence of a sol-
vent, particularly a polar solvent, can also stabilize charge
separation within the molecule. This not only changes the
energy, but also results in a shift in the electron density
and associated properties. In reality, these are the result of
the quantum mechanical interaction between solvent and
solute, which must be averaged over all possible attitudes
of solvent molecules consistent with the principles of sta-
tistical mechanics. The results of the CNT-amino acids
BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS STUDY OF AMINO ACIDS BINDING TO NANOTUBE 499
Nastaran, Saharnaz and Reza
Table 1b: Calculated Properties of C60 and binding to amino acids.
(A) Electric Potential, (B) Electrostatic Properties, (C) Total atomic charges
CNT-His-Pro CNT-Lys-Arg
Atomic
number
A B C Atomic
number
ABC
N
1
-18.421 10.12 -0.502 N
1
-18.340 6.28 -0.593
C
2
-14.757 8.93 -0.054 C
2
-14.753 7.43 -0.065
C
3
-14.713 7.67 0.321 C
3
-14.769 7.96 0.178
O
4
-22.380 7.92 -0.414 O
4
-22.375 7.54 -0.398
C
5
-14.800 9.29 -0.253 C
5
-14.751 8.66 -0.255
C
6
-14.798 10.82 -0.276 C
6
-14.732 9.86 -0.282
C
7
-14.769 11.22 -0.140 C
7
-14.652 11.10 -0.120
N
8
-18.322 6.66 -0.608 N
8
-18.228 12.30 -0.649
C
9
-14.690 7.78 -0.063 C
9
-14.496 13.51 0.863
C
10
-14.702 9.04 0.182 N
10
-18.215 13.80 -0.728
O
11
-22.316 9.14 -0.392 N
11
-18.218 14.54 -0.741
C
12
-14.694 8.25 -0.288 C
17
-14.771 6.44 -0.159
C
13
14.619 9.55 0.276 C
70
-14.761 5.38 0.052
N
14
-18.192 10.31 -0.679 N
72
-18.513 9.18 -0.514
C
15
-14.633 10.36 0.149 C
73
-14.797 8.59 -0.123
C
16
-14.564 11.42 0.411 C
74
-14.728 7.48 0.371
N
17
-18.187 11.46 -0.679 O
75
-22.350 7.22 -0.447
C
19
-14.698 5.48 0.186 C
76
-14.795 9.74 -0.236
C
73
-14.774 6.36 -0.217 C
77
-14.778 9.46 -0.234
C
78
-14.718 10.81 -0.271
C
79
-14.637 10.84 -0.207
N
80
-18.155 12.24 -0.680
Table 2: Semi empirical Calculations for CNT and conjunction to amino acids.
C60
Nanotube
C60-
Ala-Gly
C60-
Ala-Leu
C60–
Val-Ala
C60-
Gln-Asn
C60–
His-Pro
C60-
Lys-Arg
C60-
Phe-Tyr
C60-
Ser-Thr
C60-
Trp-Pro
Total Energy
(kcal/mol)
-207257 -254702 -273475 -188038 -298292 -291066 739779.4 789947 573814.9 831669.4
Binding
Energy
(kcal/mol)
-37784.3 -45141.8 -50207.3 32104.26 -52071.7 -52672.9 993483.9 1046278 804308.2 1083965
Electronic
Energy
(kcal/mol)
-2069240 -2722240 -3106366 -2914485 -3373457 -3256055 -2520644 -2590608 -2239658 -2639509
Rotation
Frequency
352.31 361.96 358.71 3773.92 352.64 369.47 251.51 1816.71 -3825.72 1864.92
Rotation
Intensity
0.064 1.285 0.347 8.368 0.315 1.969 1.6 2.669 2.892 5.153
ΔE -2283.99 -2739.14 -2895.54 -2857.42 -3154.71 -3082.21 -3235.42 -3315.58 -2967.73 -3226.15
Dipole
moment
4.1475 11.759 3.2852 8.2113 14.002 32.3063 33.2251 6.3174 6.7668 8.1059
cluster simulation can be used to analyze the energetic
aspects which are associated with the process of intro-
ducing a CNT fullerene from the gas phase into different
amino acids (Table 2 and Fig 1).
The net result clearly indicates that the process of intro-
ducing a CNT to different amino acids energetically is
remarkable. Whereas a molecular mechanics potential used
to characterize the response of a SWCNT which allows long
Nastaran, Saharnaz and Reza
500 STUDY OF AMINO ACIDS BINDING TO NANOTUBE BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS
FIGURE 1. Plotting of Calculated Properties of CNT and binding to amino
acids.
range interactions between atoms, results in Molecular
Mechanics force  e ld which indicates that potential energy
is maximum and also the potential energy will increase.
CONCLUSION
To reconstruct membranous proteins, we used simulated
nanotubes in order to transfer ions across the membrane
and transfer of ions was done successfully. In this study
the more the potential energy increases the more the
conductivity of nanochannels decreases and we chose
the least energy among nanotube and amino acid com-
plexes. And also the more energy we use, the more con-
ductivity we will have; therefore, we choose the complex
which conducts the most current. was observed most
changes of Rotation Intensity and Rotation Frequency in
the CNT-ALA-VAL and CNT-SER-THR complexes. Also
we found maximum of Dipole moment (Debye) in the
CNT-LYS-ARG and CNT-HIS-PRO complexes. Minimum
of ΔE for the CNT-PHE-TYR obtained. This way we can
simulate the channels which have hereditary defects and
are not ef ciently and can observe the fundamental cure
of the diseases.
ACKNOWLEDGEMENT
Support by the Young ResearchersandElites club, Sci-
ence and Research Branch, Islamic Azad University, Teh-
ran, Iran. is greatly acknowledged and we appreciate the
Dr Fahimeh Sadat Vajedi in Kashan University.
Nastaran, Saharnaz and Reza
BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS STUDY OF AMINO ACIDS BINDING TO NANOTUBE 501
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