alpha-Crystallin C-terminal domain: on the track of an Ig fold.

New results obtained from a two-dimensional sequence analysis of the small heat shock protein (shsp) family are described. It is confirmed that the conserved C-terminal alpha-crystallin domain is essentially made of beta-strands, most probably two groups of beta-strands separated by a large loop. A direct correspondence between the putative beta-strands that have been identified in shsps and the seven beta-strands of a classical immunoglobulin-like fold is proposed. The hypothesis that the shsp family could belong to the immunoglobulin superfamily (IgSF) is consistent with the ubiquitous distribution and the multifunctional properties of the crystallins that are now emerging.