δ-Crystallin is More Thermostable Than Mammalian Argininosuccinate Lyase

Voorter, Christina E.M.; Salemink, Irene; Jong, W.W. de

doi:10.1006/exer.1993.1091

Cited by 7 publications

(1 citation statement)

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“…crystallin relative to hASL 70.71 kcal mol Ϫ1 !, with dd1 being the least stable. These results appear to contradict the comparative experiments of Voorter et al 1993!, which suggested that dd2 crystallin is more stable than pig or bovine liver ASL~Voorter et al, 1993!. There are a number of differences between the two sets of experiments that may account for this discrepancy, the most significant of which may be the difference in the protein samples that were used.…”

Section: Stability Of D-crystallins and Haslmentioning

confidence: 58%

Domain exchange experiments in duck d‐crystallins: Functional and evolutionary implications

et al. 1999

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Abstractd-Crystallin, the major soluble protein component of the avian and reptilian eye lens, is homologous to the urea cycle enzyme argininosuccinate lyase~ASL!. In duck lenses there are two d crystallins, denoted d1 and d2. Duck d2 is both a major structural protein of the lens and also the duck orthologue of ASL, an example of gene recruitment. Although 94% identical to d20ASL in the amino acid sequence, d1 is enzymatically inactive. A series of hybrid proteins have been constructed to assess the role of each structural domain in the enzymatic mechanism. Five chimeras-221, 122, 121, 211, and 112, where the three numbers correspond to the three structural domains and the value of 1 or 2 represents the protein of origin, d1 or d2, respectively-were constructed and thermodynamically and kinetically analyzed. The kinetic analysis indicates that only domain 1 is crucial for restoring ASL activity to d1 crystallin, and that amino acid substitutions in domain 2 may play a role in substrate binding. These results confirm the hypothesis that only one domain, domain 1, is responsible for the loss of catalytic activity in d1. The thermodynamic characterization of human ASL~hASL! and duck d1 and d2 indicate that d crystallins are slightly less stable than hASL, with the d1 being the least stable. The DGs of unfolding are 57.25, 63.13, and 70.71 kcal mol Ϫ1 for d1, d2, and hASL, respectively. This result was unexpected, and we speculate that d crystallins have adapted to their structural role by adopting a slightly less stable conformation that might allow for enhanced protein-protein and protein-solvent interactions.

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Section: Stability Of D-crystallins and Haslmentioning

confidence: 58%