Abstract
Peptidases occur naturally in all organisms and their genes comprise 1–5% of the total number of genes. Genetic, biochemical, and molecular approaches used in recent years led to the identification and characterization of several plant organelle proteases, all of them being homologous to bacterial proteases best characterized in Escherichia coli. Here we report isolating and characterizing three novel genes, namely Sszn-mp1, Sszn-mp2, and SsZn-mp3 from Solanum surattense. To identify the subcellular location, structures, and functions of these three genes, integrated genomic approaches of data mining, expression profiling, and bioinformatic predictions were used. Sszn-mp is found to be constitutively expressed in tissues and regulated by various stimuli. Analysis of eight zinc-metalloproteases (Zn-MPs) deduced or assembled from Arabidopsis thaliana, tomato, potato, cotton, barley, sugarcane, and rice and four Zn-MPs from cyanobacteria (blue-green algae) in the GenBank database reveals that these proteins belong to a novel conserved membrane zinc-metalloprotease family. The plant Zn-MP members share more than 62% overall identity with SsZn-MP3, whereas four putative ATP-dependent zinc-proteases of cyanobacteria have low identity with SsZn-MP3 and their N-termini are about 110 amino acids shorter than those of plant Zn-MPs. The Zn-MP homologous sequences are found neither in other eukaryotic nor prokaryotic databases, suggesting that this family is specific to plants and cyanobacteria. The plant Zn-MP genes encoding membrane proteins are potentially targeted to chloroplast and plasma membranes, and the bacterial Zn-MPs are targeted to the cytoplasmic membrane, and their N-terminal targeting peptides are cleaved off for targeting the mature proteins to their subcellular compartments. The Zn-MP proteins contain a conserved zinc-binding site (HEAGHX19E/DX46∼48EX7E), a potential G-protein coupled receptors family 1 signature, and a triplet motif (N-R/K-F) in plant Zn-MPs, a D/E-R-Y motif in the four bacterial Zn-MPs, suggesting that the different mature forms of Zn-MPs may function as proteases and/or signal receptors.
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