MS-271, a novel inhibitor of calmodulin-activated myosin light chain kinase from Streptomyces sp.—I. isolation, structural determination and biological properties of MS-271 Original Research Article

A novel cyclic peptide, MS-271, was isolated from the culture broth of an actinomycete, Streptomyces sp. M-271 as an inhibitor of smooth muscle myosin light chain kinase (MLCK). MS-271 inhibited the MLCK from chicken gizzard with an IC50, value of 8 μM. MS-271 did not inhibit cyclic AMP-dependent protein kinase, protein kinase C or calcium/calmodulin-dependent cyclic nucleotide phosphodiesterase at concentrations up to 400 μM. The primary structure of MS-271 was identical to that of siamycin I, an anti-HIV peptide isolated from a microbial source.