Evolution of the mammalian lysozyme gene family.

David M Irwin,Jason M Biegel,Caro-Beth Stewart

doi:10.1186/1471-2148-11-166

Abstract

BackgroundLysozyme c (chicken-type lysozyme) has an important role in host defense, and has been extensively studied as a model in molecular biology, enzymology, protein chemistry, and crystallography. Traditionally, lysozyme c has been considered to be part of a small family that includes genes for two other proteins, lactalbumin, which is found only in mammals, and calcium-binding lysozyme, which is found in only a few species of birds and mammals. More recently, additional testes-expressed members of this family have been identified in human and mouse, suggesting that the mammalian lysozyme gene family is larger than previously known.ResultsHere we characterize the extent and diversity of the lysozyme gene family in the genomes of phylogenetically diverse mammals, and show that this family contains at least eight different genes that likely duplicated prior to the diversification of extant mammals. These duplicated genes have largely been maintained, both in intron-exon structure and in genomic context, throughout mammalian evolution.ConclusionsThe mammalian lysozyme gene family is much larger than previously appreciated and consists of at least eight distinct genes scattered around the genome. Since the lysozyme c and lactalbumin proteins have acquired very different functions during evolution, it is likely that many of the other members of the lysozyme-like family will also have diverse and unexpected biological properties.

Highlights

Lysozyme c has an important role in host defense, and has been extensively studied as a model in molecular biology, enzymology, protein chemistry, and crystallography
Previous phylogenetic analyses of lysozyme c, lactalbumin, and calcium-binding lysozyme sequences had suggested that the earliest divergences within this gene family occurred between lysozyme c and the ancestor of the genes for lactalbumin and calcium-binding lysozyme, and that this initial gene duplication may have preceded the divergence of the lineages leading to fish and mammals [10,11]
Number of Lysozyme Genes in the Human Genome To determine the size of the lysozyme-like gene family, we performed BLAST [20] similarity searches of the human genome for sequences that predict potential protein sequences similar to lysozyme c, and thereby identified a total of nine annotated genes (Table 1, and Additional file 1: Table S1)

Summary

Introduction

Lysozyme c (chicken-type lysozyme) has an important role in host defense, and has been extensively studied as a model in molecular biology, enzymology, protein chemistry, and crystallography. Lysozyme c has been considered to be part of a small family that includes genes for two other proteins, lactalbumin, which is found only in mammals, and calcium-binding lysozyme, which is found in only a few species of birds and mammals. The vertebrate lysozyme gene family has traditionally been considered to be composed of three genes: lysozyme c, lactalbumin, and calcium-binding lysozyme [1,2,3,4]. The separation of the lactalbumin and calcium-binding lysozyme genes was proposed to be more recent, with some studies [9,12] suggesting a divergence on the early mammalian lineage, which would be consistent with the restriction of the lactalbumin gene to mammals. Another study [11] suggested that the duplication generating the lactalbumin and calciumbinding lysozyme genes predated the bird-mammal divergence. The origin of these mammalian lysozyme-like genes remains an open question

Methods

Results

Conclusion