title: Structural divergence in vertebrate phylogeny of a duplicated prototype galectin.
abstract: Prototype galectins, endogenously expressed animal lectins with a single carbohydrate recognition domain, are well-known regulators of tissue properties such as growth and adhesion. The earliest discovered and best studied of the prototype galectins is Galectin-1 (Gal-1). In the Gallus gallus (chicken) genome, Gal-1 is represented by two homologs: Gal-1A and Gal-1B, with distinct biochemical properties, tissue expression, and developmental functions. We investigated the origin of the Gal-1A/Gal-1B divergence to gain insight into when their developmental functions originated and how they could have contributed to vertebrate phenotypic evolution. Sequence alignment and phylogenetic tree construction showed that the Gal-1A/Gal-1B divergence can be traced back to the origin of the sauropsid lineage (consisting of extinct and extant reptiles and birds) although lineage-specific duplications also occurred in the amphibian and actinopterygian genomes. Gene synteny analysis showed that sauropsid gal-1b (the gene for Gal-1B) and its frog and actinopterygian gal-1 homologs share a similar chromosomal location, whereas sauropsid gal-1a has translocated to a new position. Surprisingly, we found that chicken Gal-1A, encoded by the translocated gal-1a, was more similar in its tertiary folding pattern than Gal-1B, encoded by the untranslocated gal-1b, to experimentally determined and predicted folds of nonsauropsid Gal-1s. This inference is consistent with our finding of a lower proportion of conserved residues in sauropsid Gal-1Bs, and evidence for positive selection of sauropsid gal-1b, but not gal-1a genes. We propose that the duplication and structural divergence of Gal-1B away from Gal-1A led to specialization in both expression and function in the sauropsid lineage.
authors.affiliation: Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California rbhat@lbl.gov.
authors.forename: Ramray
authors.initials: R
authors.lastname: Bhat
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Irvine.
authors.forename: Mahul
authors.initials: M
authors.lastname: Chakraborty
authors.affiliation: Department of Computer Science, University College London, United Kingdom.
authors.forename: I S
authors.initials: IS
authors.lastname: Mian
authors.affiliation: Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York.
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Newman
mesh_terms: D000818:Animals; D037161:Galectins / Q000737:chemistry* / Q000235:genetics; D010802:Phylogeny; D017433:Protein Structure, Secondary; D014714:Vertebrates / Q000145:classification* / Q000235:genetics
chemical_list: D037161:Galectins
keywords: galectin-1; homology; protein fold; prototype galectin; sauropsids