Abstract
BackgroundMost members of the serpin family of proteins are potent, irreversible inhibitors of specific serine or cysteine proteinases. Inhibitory serpins are distinguished from members of other families of proteinase inhibitors by their metastable structure and unique suicide-substrate mechanism. Animal serpins exert control over a remarkable diversity of physiological processes including blood coagulation, fibrinolysis, innate immunity and aspects of development. Relatively little is known about the complement of serpin genes in plant genomes and the biological functions of plant serpins.ResultsA structurally refined amino-acid sequence alignment of the 14 full-length serpins encoded in the genome of the japonica rice Oryza sativa cv. Nipponbare (a monocot) showed a diversity of reactive-centre sequences (which largely determine inhibitory specificity) and a low degree of identity with those of serpins in Arabidopsis (a eudicot). A new convenient and functionally informative nomenclature for plant serpins in which the reactive-centre sequence is incorporated into the serpin name was developed and applied to the rice serpins. A phylogenetic analysis of the rice serpins provided evidence for two main clades and a number of relatively recent gene duplications. Transcriptional analysis showed vastly different levels of basal expression among eight selected rice serpin genes in callus tissue, during seedling development, among vegetative tissues of mature plants and throughout seed development. The gene OsSRP-LRS (Os03g41419), encoding a putative orthologue of Arabidopsis AtSerpin1 (At1g47710), was expressed ubiquitously and at high levels. The second most highly expressed serpin gene was OsSRP-PLP (Os11g11500), encoding a non-inhibitory serpin with a surprisingly well-conserved reactive-centre loop (RCL) sequence among putative orthologues in other grass species.ConclusionsThe diversity of reactive-centre sequences among the putatively inhibitory serpins of rice point to a range of target proteases with different proteolytic specificities. Large differences in basal expression levels of the eight selected rice serpin genes during development further suggest a range of functions in regulation and in plant defence for the corresponding proteins.
Highlights
Introduction to Protein ArchitectureOxford: Oxford University Press; 2001.48
A new rice serpin nomenclature In a detailed review of plant serpins conducted previously, each of the 14 full-length serpins encoded in the O. sativa cv
Since serpins from ~60 plant species were compared in the review, serpin names included a five-letter abbreviation for the Latin name (e.g. Orysa for Oryza sativa)
Summary
Introduction to Protein ArchitectureOxford: Oxford University Press; 2001.48. Irving JA, Pike RN, Lesk AM, Whisstock JC: Phylogeny of the serpin superfamily. Most members of the serpin family of proteins are potent, irreversible inhibitors of specific serine or cysteine proteinases. Inhibitory serpins are distinguished from members of other families of proteinase inhibitors by their metastable structure and unique suicide-substrate mechanism. Serpins have been shown to be involved in a remarkable diversity of physiological processes in humans and in distinct model animal systems [3]. Most animal serpins act biochemically as irreversible inhibitors of specific endogenous serine (less commonly cysteine) proteinases [2]. The well-studied mammalian serpin, antithrombin (SERPINC1), is an inhibitor of several of the activated forms of blood coagulation factors including thrombin (Factor IIa) as well as other serine proteinases of the chymotrypsin family [4]. The first X-ray crystal structure of a plant serpin—that of Arabidopsis thaliana AtSerpin (locus At1g47710) in the native, stressed conformation—was obtained recently and shown to be consistent with the description above but to display plant-specific features [7]
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