9.B.12 The Sensitivity to Sodium or Salt Stress-induced Hydrophobic Peptide (Sna) Family
The Sna family (referred to as the UPF0057 family by SwissProt) consists of peptides found ubiquitously in bacteria, yeast, plants and animals. There are four members of the SHP family encoded within the S. cerevisiae genome, at least eight in C. elegans and two in Synechocystis. Expression of the gene encoding one member of the SHP family, a peptide from barley or 'tall wheat grass' (L. elongatum), has been shown to be induced by both salt and low temperature stress.
Yeast (S. cerevisiae and Candida albicans) plasma membranes contain a non-essential 55 aa hydrophobic peptide (Pmp3p) with two putative TMSs and sequence similarity to a family of plant and animal proteins. One plant peptide (LT16A or RC12A; gbAAF26091) is over-expressed under high salt or low temperature conditions. One C. elegans protein (pirT26079) is large (551 aas) with the region of sequence similarity at the C-terminus, while two others (pirS40492 and T16929) are small (92 aas and 77 aas) with the region of homology at the N-terminus and the C-terminus, respectively. The PMP3 gene product in yeast possibly gives rise to hyperpolarization of the membrane potential, promoting sensitivity to cytotoxic cations such as Na+ and hygromycin B. The plant homologue, RC12A, can replace Pmp3p. These results could be explained if Pmp3p forms oligomeric pores that conduct H+ or another cation.