IC50: 0.57 μM (MMP-2), 0.25 μM (MMP-9)

Histatin 5 is a member of a family of low-molecular-weight salivary proteins secreted by parotid, submandibular, and sublingual glands. Using biotinylated gelatin as a substrate, Histatin 5 inhibits the activity of the host matrix metalloproteinases MMP-2 and MMP-9 with IC ₅₀ s of 0.57 and 0.25 μM, respectively. To localize the domain responsible for this inhibition, three peptides containing different regions of Histatin 5 are synthesized and tested as inhibitors of MMP-9. Peptides comprising residues 1 to 14 and residues 4 to 15 of Histatin 5 show much lower inhibitory activities (IC ₅₀ , 21.4 and 20.5 μM, respectively), while a peptide comprising residues 9 to 22 showed identical activity to Histatin 5 against MMP-9. Kinetic analysis of the inhibition of the Arg-gingipain reveals that Histatin 5 is a competitive inhibitor, affecting only the K _m with a K _i of 15 μM. Histatin 5 is an inhibitor of mitochondrial respiration.The human salivary antifungal peptide Histatin 5 is taken up by Candida albicans cells and associates intracellularly with mitochondria. Histatin 5 inhibits respiration of isolated C. albicans mitochondria as well as the respiration of intact blastoconidia in a dose and time-dependent manner. Histatin 5 at a concentration of 33 μM inhibits state 2 respiration.