Full text of DOI:10.1080/15216540050212123

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IUBMB Life, 50: 115 117, 2000
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Copyright 2000 IUBMB
1521-6543/00 $12.00 + .00
Original Research Article
Model of Detergent-Induced Spectral Changes of the
Chromatium minutissimum
B800–850 Complex from
Andrei P. Razjivin,1 Andrei A. Moskalenko,2 and Vladimir I. Novoderezhkin1
1A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow
119899, Russian Federation
2Institute of Basic Biological Problems, Russian Academy of Sciences, Puschino, Moscow Region,
142292, Russian Federation
In this paper we have simulated the absorption and circular
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(
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dichroic CD spectra of the B800 850 complex from Chro-
matium minutissimum before and after treatment with Triton
Summary
The absorption and circular dichroism spectra of the B800–850
complex from Chromatium minutissimum before and after the Tri-
ton X-100 treatment were simulated by means of standard exciton
theory, taking into account inhomogeneous broadening. To explain
the spectral changes of the B800–850 complex treated with Triton
X-100, we have assumed that all bacteriochlorophyll pigments ab-
sorbing at 850 nm exhibit the same additional rotation of « 20±
around the axis perpendicular to the membrane plane. This has
been sufŽ cient to Ž t the transformation in absorption and circular
dichroism spectra induced by detergent treatment of the B800–850
complex.
(
)
]
[
X-100 detergent. As in our previous publications e.g., 5, 6 ,
we use the standard exciton theory, taking into account inhomo-
geneous broadening.
EXPERIMENTAL PROCEDURES
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The pigment protein complex B800 850 from C. minutissi-
mum strain MSU was isolated by means of preparative elec-
trophoresis in polyacrylamide gel as described previously 7, 8 .
Absorption spectra were measured with a Model UV-160
Shimadzu spectrophotometer. CD spectra were monitored with
a homemade spectrometer.
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IUBMB
Life, 50: 115 117, 2000
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Keywords B800 850 complex; Chromatium minutissimum; confor-
mationtransition;excitontheory; spectralchanges;Triton
X-100.
MODEL OF THE LH2 ANTENNA
INTRODUCTION
The LH2 complexes contain two polypeptides, a and b,
Detergents as well as solvents, salts, and other agents are well
known to affect the spectral properties of the peripheral light-
(
) ( )
which bind bacteriochlorophyll BChl 9 . We suppose that
the pigment organization in LH2 of C. minutissimum is anal-
ogous to that of the LH2 antenna from Rhodopseudomonas aci-
harvesting pigment protein complex LH2 or B800 850 3 from
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–
(
)
–
(
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purple photosynthetic bacteria 1 4 . In particular, the spectral
position of the long-wavelength absorption band of the B800
850 complex may be tuned within the 830 850 nm range by
detergent treatment 3, 4 .
(
)
dophila 10 . For a model of an antenna unit, we consider two
concentric circular aggregates that lie in two planes parallel to
the membrane plane. The Ž rst aggregate consists of n strongly
coupled BChl850 molecules and has the Cn/2-symmetry with
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–
(
)
a dimeric unit cell. The second ring consists of n 2 weakly
/
coupled BChl800 molecules and has the Cn/2-symmetry with
Received 24 April 2000; accepted 26 May 2000.
a monomeric unit cell. We assume n
18. The Qy transition
=
(
)
Address correspondence to Andrei Razjivin. Fax: 07-095 939-
3181. E-mail: razjivin@genebee.msu.su
dipole moments of two BChls in a dimeric unit cell form angles
w1, w2 with the ring plane and angles }1, }2 with the tangent
to the circle. The energies of electronic transitions of these two
BChls are E1 and E2, respectively.0The corresponding param-
3Abbreviations: B800, B850, bacteriochlorophyll absorption band with the
peak at 800 or 850 nm, respectively; BChl, bacteriochlorophyll; BChl800,
BChl850, bacteriochlorophyll spectral form with the absorption peak at 800
–
or 850 nm, respectively; CD, circular dichroism; LH2 or B800 850 complex,
the peripheral light-harvesting complex of purple photosynthetic bacteria having
absorption peaks at 800 and 850 nm.
0
0
–
eters for BChl800 pigments are w , } , and E . The Mg Mg
distances between BChls were taken to be the same as for LH2
115

116
RAZJIVIN ET AL.
(
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(
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Figure 1. Absorption top and CD bottom spectra of the Figure 2. Same as in Fig. 1, but experimental spectra obtained
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B800 850 complex from C. minutissimum in phosphate buffer, after treatment of the B800 850 complex with 0.8% Triton
pH 8.0, at room temperature. Points, experimental data; dashed X-100. Calculated spectra were obtained by supposing each
curve, calculated absorption and CD proŽ les; solid lines, cal- BChl850 molecule rotated at 20± around the axis perpendi-
«
(
culated absorption line shapes for individual exciton com- cular to the membrane plane and with adjusted line-broadening
)
parameters; see text .
ponents.
–
of R. acidophila. In our simulations of the B800 850 absorp- dE of electronic energies of BChl800 and BChl850 pigments,
tion and CD spectra, we have taken into account the interactions E0 and E. We assumed that dE0 and dE have a gaussian distri-
(
)
between the Qy transitions of BChls, neglecting their mixing bution. The width full width at half-maximum, FWHM of this
with Qx , By, and Bx transitions as well as the charge transfer distribution is r0 and r.
states.
To calculate absorption and CD spectra, we used the method
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The interaction energies were calculated in the dipole dipole of direct numerical diagonalization of one-exciton Hamiltonian
approximation by supposing that the monomeric dipole strength and Monte Carlo averaging over a random distribution of dia-
is equal to 40 D2. The nearest neighbor interaction energies were gonal energies modeling the site inhomogeneity. We used the
–
–
reduced by 20% because of deviation from the dipole dipole standard Hamiltonian for the Frenkel exciton in the Heitler
(
)
approximation at short distances. The site inhomogeneity of the London approximation for two-level molecules 11 . To cal-
antenna was described by uncorrelated perturbations dE0 and culate the homogeneously broadened spectra for each set of
(

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117
MODEL OF SPECTRAL CHANGES OF THE B800 850 COMPLEX
)
diagonal energies , we assumed the Lorentzian line shape. The ACKNOWLEDGEMENTS
(
)
homogeneous line widths FWHM are CM for exciton levels of
This work was supported in part by grants INTAS-96-1435
and Russian Foundation for Basic Research 00-04-48308.
(
)
(
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the B800 band, and C1L C1H for the lowest higher exciton
levels of the B850 band.
REFERENCES
1. Miller, J. F., Hinchigeri, S. B., Parkes-Loach, P. S., Callahan, P. M.,Sprinkle,
RESULTS AND DISCUSSION
The measured and calculated spectra are shown in Figs. 1
and 2. The best Ž t for the B800 850 complex Fig. 1 was ob-
(
)
J. R.,Riccobono, J. R.,and Loach, P. A. 1987 Isolation and characterization
of a subunit formof the light-harvesting complex of Rhodospirillum rubrum.
–
Biochemistry 26, 5055 5062.
–
(
)
(
)
2. Jursakova, V., and Reiss-Husson, F. 1993 Isolation and characterisation of
tained for w1 2±, w
2±, }
195±, }
= ¡
25±, w0 9±,
= =
=
= ¡
=
2
1
2
the core light-harvesting complex B875 and its subunit form, B820, from
0
}
185±, E1
470 cm¡1, E2
270 cm¡1, E0
=
=
= ¡
–
Rhodocyclus gelatinosus. Biochim. Biophys. Acta 1183, 301 308.
250 cm¡1 transition energies are calculated from the tran-
3. Sturgis, J. N., Hagemann, G., Tardos, M. H., and Robert, B. 1995 Biochem-
(
(
)
¡
–
ical and spectroscopic characterization of the B800 850 light-harvesting
sition energy of a BChl a monomer, which corresponds to k
=
–
complex from Rhodobacter sulphidophilus and its B800 830 spectral form.
777 nm , CM 160 cm¡1, C1L 250 cm¡1, C1H 340 cm¡1
,
)
=
=
=
–
Biochemistry 34, 10519 10524.
r
500 cm¡1, and r0 340 cm¡1
.
–
=
=
4. Moskalenko, A. A., Kuznetsova, N. Yu., Erokhin, Yu. E., and Toropy-
To Ž t the spectra for the B800 850 complex treated with
(
)
gina, O. A. 1996 Structural peculiarities and conformational transitions
–
1% Triton X-100, we supposed that both BChl850 pigments in
of the B800 850 complex from Chromatium minutissimum. Biochemistry
a dimeric subunit show additional rotation of 20± from the
–
–
(
)
Moscow 61, 318 325. Translated from Biokhimiya 61, 429 439.
5. Novoderezhkin, V. I., and Razjivin A. P. 1995 Exciton dynamics in cir-
cular aggregates: application to antenna of photosynthetic purple bacteria.
Biophys. J. 68, 1089 1100.
6. Dracheva, T. V., Novoderezhkin, V. I., and Razjivin, A. P. 1997 Exciton
delocalization in the light-harvesting LH2 complex of photosynthetic purple
bacteria. Photochem. Photobiol. 66, 141 146.
7. Moskalenko, A. A., and Toropygina, O. A. 1988 Study of relationship
«
(
)
(
tangent to the circle; that is, }1
215±, }2
45± all other
=
=
)
parameters are the same . This is sufŽ cient to describe the ab-
sorption and CD spectra transformation after the detergent treat-
ment. A better quantitative Ž t may be obtained if we suppose
–
(
)
–
(
also some increase of static and dynamic disorder increase of
(
)
)
inhomogeneous and homogeneous broadening , which yields
–
between the light-harvesting complex B800 850 to the H-subunit of the
reaction center in sulfur photosynthetic bacterium Chromatium minutissi-
mum. Biokhimiya 53, 1220 1223 in Russian .
CM
560 cm¡1, r0 440 cm¡1 see Fig. 2 .
190 cm¡1, C1L 320 cm¡1, C1H 420 cm¡1, r
=
=
=
=
(
)
=
–
(
)
(
)
A hypothetical scheme for the conformational transitions in
8. Moskalenko, A. A., and Erokhin, Yu. E. 1974 Isolation of pigment-
lipoprotein complexes from purple photosynthesizing bacteria by the
method of polyacrylamide gel electrophoresis In Russian . Mikrobiologiia
–
the B800 850 complex from C. minutissimum when treated
(
)
with various agents including Triton X-100 has been pro-
–
43, 654 658.
( )
posed previously 4 . According to that scheme, the spatial ar-
(
)
9. Zuber, H. 1985 Structure of antenna polypeptides. In Antennas and Re-
rangement of the C-terminal ends of a-helices bearing BChl
molecules is altered by Triton X-100 treatment, which results
in disturbance of pigment interactions inside the BChl long-
wavelength spectral form. The calculations presented here show
that the corresponding spectral changes may be modeled by
(
)
action Centers of Photosynthetic Bacteria Michel-Beyerly, M. E., ed. .
–
pp. 2 14, Springer-Verlag, Berlin.
10. McDermott, G., Prince, S. M., Freer, A. A., Hawthornthwaite-Lawless,
(
)
A. M., Papuz, M. Z., Cogdell, R. J., and Isaacs, N. W. 1995 Crystal struc-
ture of an integral membrane light-harvesting complex from photosynthetic
–
bacteria. Nature 374, 517 521.
–
the small rotation of each BChl850 molecule in the B800 850
(
)
11. Davydov, A. S. 1971 Theory of Molecular Excitons. Plenum Press,
complex.
New York.

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