Mast Cell α and β Tryptases Changed Rapidly during Primate Speciation and Evolved from γ-Like Transmembrane Peptidases in Ancestral Vertebrates

Abstract

Human mast cell tryptases vary strikingly in secretion, catalytic competence, and inheritance. To explore the basis of variation, we compared genes from a range of primates, including humans, great apes (chimpanzee, gorilla, orangutan), Old- and New-World monkeys (macaque and marmoset), and a prosimian (galago), tracking key changes. Our analysis reveals that extant soluble tryptase-like proteins, including α- and β-like tryptases, mastins, and implantation serine proteases, likely evolved from membrane-anchored ancestors because their more deeply rooted relatives (γ tryptases, pancreasins, prostasins) are type I transmembrane peptidases. Function-altering mutations appeared at widely separated times during primate speciation, with tryptases evolving by duplication, gene conversion, and point mutation. The α-tryptase Gly216Asp catalytic domain mutation, which diminishes activity, is present in macaque tryptases, and thus arose before great apes and Old World monkeys shared an ancestor, and before the αβ split. However, the Arg−3Gln processing mutation appeared recently, affecting only human α. By comparison, the transmembrane γ-tryptase gene, which anchors the telomeric end of the multigene tryptase locus, changed little during primate evolution. Related transmembrane peptidase genes were found in reptiles, amphibians, and fish. We identified soluble tryptase-like genes in the full spectrum of mammals, including marsupial (opossum) and monotreme (platypus), but not in nonmammalian vertebrates. Overall, our analysis suggests that soluble tryptases evolved rapidly from membrane-anchored, two-chain peptidases in ancestral vertebrates into soluble, single-chain, self-compartmentalizing, inhibitor-resistant oligomers expressed primarily by mast cells, and that much of present numerical, behavioral, and genetic diversity of α- and β-like tryptases was acquired during primate evolution.

Mutational Tail Loss Is an Evolutionary Mechanism for Liberating Marapsins and Other Type I Serine Proteases from Transmembrane Anchors

“…Human and mouse marapsin genes and cDNAs (10) were used as query sequences. Previously unreported amino acid sequences of marapsins and marapsin-like proteases were predicted from genomic DNA using existing human and mouse gene structures as a template following standard rules for placement of intron-exon boundaries as detailed in prior publications involving phylogenetic studies of related serine proteases (5,7,8,10). Resulting protein sequences were aligned using Geneious software (Biomatters, Auckland, New Zealand).…”

“…On the C-terminal end, aligned sequences were cut off at conserved His 239 of marapsin (or equivalent residue in related proteases) to avoid biasing effects of length variations in protease C termini, which do not universally include a membrane-spanning domain, which can extend protease sequence by 30 or more residues. A rooted tree was generated by unweighted pair group with arithmetic mean analysis using methods described previously (7).…”

“…1, marapsins (as deduced from genomic or cDNA sequence) are present in a wide variety of placental and marsupial mammals and in reptiles. The breadth of representation in mammalian genomes is similar to that of prostasin (7,22), a related enzyme that is essential for embryonic development and postnatal survival in mice (23,24). Marapsin genes are more widespread than those that encode ␥-tryptase, which is absent from genomes of dogs and several other mammals and lacks an identified ortholog in non-mammalian vertebrates (7,9).…”

“…The breadth of representation in mammalian genomes is similar to that of prostasin (7,22), a related enzyme that is essential for embryonic development and postnatal survival in mice (23,24). Marapsin genes are more widespread than those that encode ␥-tryptase, which is absent from genomes of dogs and several other mammals and lacks an identified ortholog in non-mammalian vertebrates (7,9). Marapsin catalytic domain sequence conservation is high in comparison with related enzymes like testisin and ␥-tryptase as reflected by cladogram tine length, which is proportional to the number of sequence mismatches between a given pair of sequences.…”

“…Seeking such evidence, we focused on marapsin (also known as pancreasin and PRSS27), which belongs to a group of serine proteases featuring members that can be either soluble or type I transmembrane proteins but are otherwise closely related (e.g. human versus mouse (10)) with highly conserved catalytic domains in mammals and some other vertebrates (7,11). Marapsins, therefore, provide an opportunity to test the hypothesis that some soluble serine proteases evolved from membrane-anchored proteases and to explore genetic mechanisms of the conversion.…”