Zinc binding in bovine α-lactalbumin: Sequence homology may not be a predictor of subtle functional features
✍ Scribed by Serge E. Permyakov; Dmitry B. Veprintsev; Charles L. Brooks; Eugene A. Permyakov; Lawrence J. Berliner
- Book ID
- 101227622
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 143 KB
- Volume
- 40
- Category
- Article
- ISSN
- 0887-3585
No coin nor oath required. For personal study only.
✦ Synopsis
␣-Lactalbumin (␣-LA), a calciumbinding protein, also possesses zinc-binding sites comprising a single strong site and several weaker secondary sites. The only site found by X-ray crystallography (Ren et. al., J. Biol. Chem. 1993;268:19292) was Glu 49 of human ␣-LA, but zinc binding had never been measured in solution for human ␣-LA. This residue was genetically substituted by Ala in bovine ␣-LA and the metal-binding properties of the resulting desMetE49A protein were compared with those for native ␣-LA by fluorescence methods. Surprisingly, desMetE49A ␣-LA and the native bovine protein had similar affinities for both Zn 2؉ and Ca 2؉ . Genetic substitution of other possible candidates for Zn 2؉ chelating residues, which included Glu 25, did not alter the affinity of bovine ␣-LA to Zn2؉; however, substitution of Glu 1 by Met resulted in the disappearance of strong Zn 2؉ binding. A proposed site involves Glu 1, Glu 7, Asp 11, and Asp 37, which would participate in strong Zn 2؉ binding based on their propinquity to Glu 1. Human ␣-LA, which has a Lys at position 1 rather than Glu, binds zinc with a reduced affinity compared with native bovine ␣-LA, suggesting that the site identified from the X-ray structure did not correspond to strong zinc binding in solution. Proteins 2000;40:106 -111.