Identification and characterization of human SLP-2, a novel homologue of stomatin (Band 7.2b) present in erythrocytes and other tissues

Human stomatin (band 7.2b) is a 31-kDa erythrocyte membrane protein of unkn own function but implicated in the control of ion channel permeability, mec hanoreception, and lipid domain organization, Although absent in erythrocyt es from patients with hereditary stomatocytosis, stomatin is not linked to this disorder. A second stomatin homologue, termed SLP-1, has been identifi ed in nonerythroid tissues, and other stomatin related proteins are found i n Drosophila, Caenorhabditis elegans, and plants. We now report the cloning and characterization of a new and unusual stomatin homologue, human SLP-2 (Stomatin-like protein 2), SLP-2 is encoded by an similar to 1.5-kilobase m RNA (GenBank(TM) accession no. AF190167). The gene for human SLP-2, HUSLP2, is present on chromosome 9p13. Its derived amino acid sequence predicts a 38,537-kDa protein that is overall similar to 20% similar to human stomatin . Northern and Western blots for SLP-I and SLP-2 reveal a wide but incomple tely overlapping tissue distribution. Unlike SLP-1, SLP-2 is also present i n mature human erythrocytes (similar to 4,000 +/- 5,660 (+/- 2 S.D.) copies /cell). SLP-2 lacks a characteristic NH2-terminal hydrophobic domain found in other stomatin homologues and (unlike stomatin) is fully extractable fro m erythrocyte membranes by NaOH, pH 11. SLP-2 partitions into both Triton X -100-soluble and -insoluble pools in erythrocyte ghost membranes or when ex pressed in cultured COS cells and migrates anomalously on SDS-polyacrylamid e gel electrophoresis analysis with apparent mobilities of similar to 45,50 0, 44,600, and 34,300 M-r,. The smallest of these protein bands is believed to represent the product of alternative translation initiated at AUGs begi nning with nt 217 or 391, although this point has not been rigorously prove n. Collectively, these findings identify a novel and unusual member of the stomatin gene superfamily that interacts with the peripheral erythrocyte cy toskeleton and presumably other integral membrane proteins but not directly with the membrane bilayer, We hypothesize that SLP-2 may link stomatin or other integral membrane proteins to the peripheral cytoskeleton and thereby play a role in regulating ion channel conductances or the organization of sphingolipid and cholesterol-rich lipid rafts.