Characteristics of super alphaA-crystallin, a product of in vitro exon shuffling.

alphaA-Crystallin, a small heat shock protein with chaperone-like activity, forms dynamic multimeric complexes. Recently we described the spontaneous generation of a mutant protein (super alphaA-crystallin) by exon duplication arisen via exon shuffling confirming a classic hypothesis by Gilbert [Nature 271 (1978) 501]. Comparison of super alphaA-crystallin, which is viable in a mouse skeletal muscle cell line, with normal alphaA-crystallin shows that it has diminished thermostability, increased exposure of hydrophobic patches, a larger complex size and lost its chaperone activity. However, super alphaA-crystallin subunits exchange as readily between complexes as does normal alphaA-crystallin. These data indicate that chaperone-like activity may vanish independent of subunit hydrophobicity and exchangeability.