Trivedi Neil N, Raymond Wilfred W, Caughey George H
Cardiovascular Research Institute of the University of California at San Francisco, San Francisco, CA, USA.
J Allergy Clin Immunol. 2008 May;121(5):1262-8. doi: 10.1016/j.jaci.2008.01.019. Epub 2008 Mar 5.
Tryptases are serine peptidases stored in mast cell granules. Rodents express 2 soluble tryptases, mast cell proteases (MCPs) 6 and 7. Human alpha- and beta-tryptases are orthologs of MCP-6. However, much of the ancestral MCP-7 ortholog was replaced by parts of other tryptases, creating chimeric delta-tryptase. Human delta-tryptase's limited activity is hypothesized to be due to truncation and processing mutations.
We sought to probe the origins and consequences of mutations in primate delta-tryptases.
Prosimian (lemur), monkey (macaque), great ape (orangutan, gorilla, and chimpanzee), and human delta-tryptase genes were identified by means of data mining and genomic sequencing. Resulting genes were analyzed phylogenetically and structurally.
The seminal conversion event generating the delta-tryptase chimera occurred early because all primates studied contain delta-tryptase genes. Truncation, resulting from a nonsense mutation of Trp206, occurred much later, after orangutans and other great apes last shared an ancestor. The Arg-3Gln propeptide mutation occurred most recently, being present in humans and chimpanzees but not in other primates. Surprisingly, the major active tryptase in monkeys is full-length delta-tryptase, not beta-tryptase, which is the main active tryptase in human subjects. Models of macaque delta-tryptase reveal that the segment truncated in human subjects contains antiparallel beta-strands coursing through the substrate-binding cleft, accounting for truncation's drastic effect on activity.
Transformations in the ancestral MCP-7-like gene during primate evolution caused dramatic variations in function. Although delta-tryptases are nearly inactive in humans, they are active and dominant in monkeys.
类胰蛋白酶是储存于肥大细胞颗粒中的丝氨酸蛋白酶。啮齿动物表达2种可溶性类胰蛋白酶，即肥大细胞蛋白酶（MCP）6和7。人类α-和β-类胰蛋白酶是MCP-6的直系同源物。然而，原始MCP-7直系同源物的大部分被其他类胰蛋白酶的部分所取代，从而产生了嵌合δ-类胰蛋白酶。据推测，人类δ-类胰蛋白酶活性有限是由于截短和加工突变所致。
我们试图探究灵长类动物δ-类胰蛋白酶突变的起源及后果。
通过数据挖掘和基因组测序鉴定原猴亚目（狐猴）、猴（猕猴）、类人猿（猩猩、大猩猩和黑猩猩）及人类的δ-类胰蛋白酶基因。对所得基因进行系统发育和结构分析。
产生δ-类胰蛋白酶嵌合体的关键转化事件发生得较早，因为所有研究的灵长类动物都含有δ-类胰蛋白酶基因。色氨酸206无义突变导致的截短发生得晚得多，是在猩猩和其他类人猿最后拥有共同祖先之后。精氨酸3谷氨酰胺前肽突变是最近才出现的，存在于人类和黑猩猩中，而其他灵长类动物中没有。令人惊讶的是，猴子体内主要的活性类胰蛋白酶是全长δ-类胰蛋白酶，而非人类受试者体内主要的活性类胰蛋白酶β-类胰蛋白酶。猕猴δ-类胰蛋白酶模型显示，人类受试者体内截短的片段含有贯穿底物结合裂隙的反平行β-链，这解释了截短对活性产生的显著影响。
灵长类动物进化过程中原始MCP-7样基因的转变导致了功能上的巨大差异。虽然δ-类胰蛋白酶在人类中几乎无活性，但在猴子中却是有活性且占主导地位的。
