BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
246, 441–445 (1998)
ARTICLE NO.
RC988640
Intermolecular Interaction of Lens Crystallins:
From Rotationally Mobile to Immobile States
at High Protein Concentrations
Jack J-N. Liang*
,1
and Bireswar Chakrabarti†
,2
*Ophthalmic Research, Brigham and Women’s Hospital, and †Schepen Eye Research Institute
and Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts 02115
Received March 24, 1998
The vertebrate lens contains a high concentration of
The conformation of lens crystallins in vivo or in a
structural proteins, consisting of a family of three pro-
highly concentrated solution is not well established.
teins designated as
a
-,
b
-and
g
-crystallins. The specific
Most studies were carried out in dilute solutions in
function for each individual crystallin in the lens has
which protein-protein interaction is minimal. In order
not been clearly established, but they are thought to
to see whether there is conformational change (ter-
participate in a supramolecular organization that pro-
tiary and secondary structures) when crystallin solu-
vides the basis for lens transparency (1). A short-range
tions are brought to high concentrations, we have per-
orderamongcrystallinssufficientto maintainlenstrans-
formed the following molecular spectroscopic mea-
parency was proposed (2,3). In this model, the major
surements: circular dichroism (CD) and Fourier
crystallin,
a
-crystallin, was considered a non-penetrable
transform infrared (FTIR). Near-UV CD measurements
hard-sphere and the interactions were considered
showed a more than two-fold increase in CD intensity
mainly repulsive (4). Similar repulsive interactions were
(molar ellipticity) for the total water-soluble (WS) pro-
suggested for
b
-crystallin, but a non-specific attractive
tein from young calf lens nucleus in a highly concen-
interaction was predominant in
g
-crystallin (4,5). These
trated solution (ú300 mg/ml in a 0.01-mm cell), when
compared with a dilute solution (1000-fold dilution in a
studies suggested a progressive closer packing of lens
10-mm cell). The individual crystallins in concentrated
proteins with increasing concentrations but did not show
solutions also showed an increase in CD intensity, but
a periodic structure or a structural reorganization. A
of different magnitude:
a
-crystallin ú
b
-crystallin ú
g
-
nonspecific interaction, either homo- or hetero-molecu-
crystallin. The increased CD indicates that lens crys-
lar, in concentrated crystallin solutions was also reported
tallins are in a more compact structure in highly con-
from an ammonia gas sorption-desorption study (6) and
centrated solutions; they likely undergo a transition
polarization measurements (7). In a highly concentrated
from a mobile to an immobile state. Change in near-UV
protein solution or in the lens, an excluded volume effect
CD usually is caused by restricted mobility of aromatic
(8) causes protein to adopt a more compact structure.
side groups, particularly Trp. The transition involves
This may be inferred from the spectral change that oc-
not only a change in protein tertiary and/or quater-
curs when protein concentration is brought to a high
nary structure, but also inprotein backbone structure.
level. A nuclear magnetic relaxation dispersion (NMRD)
The change of protein backbone structure was drawn
study suggested that at a concentration above 15-19%
from FTIR measurements. FTIR spectra, sensitive to
(v/v) lens proteins interacted to produce a large aggre-
the secondary structure in the amide I region, could be
gate with a distinctly different three-dimensional organi-
measured for a highly concentrated solution for which
zation; below this concentration the lens proteins be-
far-UV CD measurement is not feasible. The secondary
haved as globular proteins (9,10). The authors suggested
structure that showed prominent change for
a
-crys-
that there was a transition from a mobile to an immobile
tallin in a highly concentrated solution was
b
-confor-
mation: increase in
b
-turn with a concomitant de-
phase at this concentration. An earlier report of
13
C high-
crease of
a
-helix structure.
᭧ 1998 Academic Press
resolution nuclear magnetic resonance measurements of
bovine lens homogenates also suggested the existence of
mobile liquid-like and slow solid-like protein tumbling
fractions (11). A similar conclusion was drawn recently
1
To whom correspondence should be addressed at Ophthalmic Re-
by
1
H NMR studies, in which the resonance from flexible
search, Brigham and Women’s Hospital, 221 Longwood Ave., Boston,
terminal extensions was probed to determine the pres-
MA 02115. Fax: 617-278-0556. E-mail: jliang@bustoff.bwh.harvard.edu.
2
Deceased.
ence or absence of crystallin-crystallin interaction (12).
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