An avian alpha B-crystallin. Non-lens expression and sequence similarities with both small (HSP27) and large (HSP70) heat shock proteins.

alpha B-crystallin is multifunctional, serving as both a major structural protein in the lens and a small heat-shock protein (shsp) in other tissues in mammals. Cloning and Northern analysis show similarly that alpha B-crystallin mRNA is present in all mature tissues examined in a bird (Anas platyrhynchos), although there are some differences in the pattern of transcripts seen. Interestingly, sequence analysis not only shows that duck alpha B-crystallin is a member of the shsp family, as expected, but that this family shares more distant similarity with another heat shock protein family, the highly conserved HSP70s of both eukaryotes and prokaryotes. This raises the possibility that large and small hsps may share structural and perhaps functional features.