Evolution of murine ?1-proteinase inhibitors: Gene amplification and reactive center divergence

Abstract

The organization and sequence of genes encoding the alpha 1-proteinase inhibitor (alpha 1PI), a major serine proteinase inhibitor of the mammalian bloodstream, have been compared in several species, including murine rodents (genus Mus). Analysis of gene copy number indicates that amplification of alpha 1PI genes occurred at some time during evolution of the Mus genus, leading to fixation of a family of about three to five genes in several existing species (e.g., M. domesticus and M. saxicola), and only a single gene in others (e.g., M. caroli). A phylogeny for the various mammalian alpha 1PI mRNAs was constructed based upon synonymous substitutions within coding regions. The mRNAs in different murine species diverged from a common ancestor before the formation of the first species lineages of the Mus genus, i.e., about 10-13 million years ago. Thus, alpha 1PI gene amplification must have occurred prior to Mus speciation; gene families were retained in some, but not all, murine species. The reactive center region of the alpha 1PI polypeptide, which determines target protease specificity, has diverged rapidly during evolution of the Mus species, but not during evolution of other mammalian species included in the analysis. It is likely that this accelerated evolution of the reactive center, which has been noted previously for serine proteinase inhibitors, was driven by some sort of a positive Darwinian selection that was exerted in a taxon-specific manner. We suggest that evolution of alpha 1PI genes of murine rodents has been characterized by both modification of gene copy number and rapid reactive center divergence. These processes may have resulted in a broadened repertoire of proteinase inhibitors that was evolutionarily advantageous during Mus speciation.

Organization of Serpin Gene-1 from Manduca sexta

“…We have expressed the serpin-1 variants as recombinant proteins and found proteinase inhibitor activity for 11 of the 12 reactive sites. 3 The individual variants can inhibit enzymes with chymotrypsin-, elastase-, or trypsin-like specificities. Serpins in insect hemolymph might inhibit proteinases produced by pathogenic microorganisms.…”

“…Comparisons of serpin sequences have demonstrated that the reactive site loop and adjacent sequence is the least conserved region of the proteins. It has been suggested that after duplications of serpin genes, rapid evolutionary change of the reactive site loop region provides new inhibitor selectivities that may have value during natural selection (2,3).…”

A 370-kb Cosmid Contig of the Serpin Gene Cluster on Human Chromosome 14q32.1: Molecular Linkage of the Genes Encoding α1-Antichymotrypsin, Protein C Inhibitor, Kallistatin, α1-Antitrypsin, and Corticosteroid-Binding Globulin

“…5) overlap by approximately 1 kb. Thus, well-characterized molecular clones containing the two for target proteinases-is hypervariable, and it has evolved much more rapidly than other parts of the proserpin gene subclusters, as well as the entire region between them, are now available; these should be use-tein (Hill and Hastie, 1987;Inglis and Hill, 1991;Rheaume et al, 1994). ful for functional studies of the region.…”

“…Krauter, 1991;Goodwin et al, 1996). Similarly, there One approach to studying the evolution of the serpin is 1 AACT gene in the human genome, whereas its superfamily has been to compare the primary se-murine counterpart, the Spi-2 locus, comprises 10 quences (Hill and Hastie, 1987; Borriello and Krauter, tightly linked genes in 129/St mice (Inglis and Hill, 1991;Inglis and Hill, 1991;Rheaume et al, 1994;Good-1991).…”

“…The cosmid contig that contains the proximal serpin gene subcluster as well as the region between the two Carrell, 1989;Marshall, 1993) of various serpin proteins. These studies indicate that the three-dimensubclusters is shown in Fig.…”