Binary-liquid phase separation of lens protein solutions

We have determined the coexistence curves (plots of phase-separation temperature T versus protein concentration C) for aqueous solutions of purified calf lens proteins. The proteins studied, calf gamma IIIa-, gamma IIIb-, and gamma IVa-crystallin, have very similar amino acid sequences and three-dim...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 1991-07, Vol.88 (13), p.5660-5664
Main Authors: BROIDE, M. L, BERLAND, C. R, PANDE, J, OGUN, O. O, BENEDEK, G. B
Format: Article
Language:English
Subjects:
Analytical, structural and metabolic biochemistry
Animals
Biological and medical sciences
Cattle
Chemical Phenomena
Chemistry, Physical
crystallins
Crystallins - chemistry
Crystallins - isolation & purification
Crystallography
eye lens
Fundamental and applied biological sciences. Psychology
General aspects, investigation methods
Hydrogen-Ion Concentration
In Vitro Techniques
Proteins
Solutions
Temperature
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Summary:We have determined the coexistence curves (plots of phase-separation temperature T versus protein concentration C) for aqueous solutions of purified calf lens proteins. The proteins studied, calf gamma IIIa-, gamma IIIb-, and gamma IVa-crystallin, have very similar amino acid sequences and three-dimensional structures. Both ascending and descending limbs of the coexistence curves were measured. We find that the coexistence curves for each of these proteins and for gamma II-crystallin can be fit, near the critical point, to the function /(Cc-C)/Cc/ = A [(Tc - T)/Tc]beta, where beta = 0.325, Cc is the critical protein concentration in mg/ml, Tc is the critical temperature for phase separation in K, and A is a parameter that characterizes the width of the coexistence curve. We find that A and Cc are approximately the same for all four coexistence curves (A = 2.6 +/- 0.1, Cc = 289 +/- 20 mg/ml), but that Tc is not the same. For gamma II- and gamma IIIb-crystallin, Tc approximately 5 degrees C, whereas for gamma IIIa- and gamma IVa-crystallin, Tc approximately 38 degrees C. By comparing the published protein sequences for calf, rat, and human gamma-crystallins, we postulate that a few key amino acid residues account for the division of gamma-crystallins into low-Tc and high-Tc groups.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.88.13.5660