The lipocalin protein family: structural and sequence overview

Lipocalins are remarkably diverse at the sequence level yet have highly con served structures. Most lipocalins share three characteristic conserved seq uence motifs - the kernel lipocalins - while others are more divergent fami ly members - the outlier lipocalins - typically sharing only one or two. Th is classification is a useful tool for analysing the family, and within the se large sets are smaller groups sharing much higher levels of sequence sim ilarity. The lipocalins are also part of a larger protein superfamily: the calycins, which includes the fatty acid binding proteins, avidins, a group of metalloproteinase inhibitors, and triabin. The superfamily is characteri sed by a similar structure (a repeated +1 topology beta -barrel) and by the conservation of a remarkable structural signature. (C) 2000 Elsevier Scien ce B.V. All rights reserved.