Identification of Serine 138 Residue in the 4-residue Segment K 135 K 136 I 137 S 138 of LukS-I Component of Staphylococcus Leukocidin Crucial for the LukS-I-specific Function of Staphylococcal Leukocidin intermedius

Luk-I pToduced by Staphylocoecus intermedius was found to be a new member of the staphylococcal bi-component pore-forming toxin family, in which staphylococcal [eukocidin, Panton-Valentine leukocidin, and 7-hemo]ysin are included. Luk-I consists of LukS-I and LukF-I. Frem the deduced amino acid sequence of LukS-I, a 4-resid"e sequence, K135K136I137S138, at the root of the stem region was found to be identical with that of the phosphorylated segment of a protein phosphorylated by protein kinase A. A mutant of LukS-I (MLSI-SA), in which the Ser138 residue was rep]aced by an a]anine residue, was created, purified, and assayed for its leukocytolytic and poreforming activities with LukF-I. Both LnkS-I and MLSISA formed a ring-shaped complex with LukF-I on rabbit erythrocytes and human polymorphonuclear leukocytes (HPMNLs) membrane. However, MLSI-SA showed no le"kocytolytic actiyity with LukF-I. LukS-I was phosphorylated by protein kinase A in the presence