Degradation of antimicrobial histatin-variant peptides in Staphylococcus aureus and Streptococcus mutans.

Histidine-free variants of salivary histatin 5 have a broad antimicrobial activity against various bacteria. In relation to a possible therapeutic application, we were interested in the susceptibility of these small peptides (14 amino acids long) to microbial proteinases and whether this affects their antimicrobial activity. Analyses by SDS-PAGE of supernatants of peptide-bacteria incubation showed a reduction in protein bands within 15 minutes' incubation, as a result of cellular internalization. Degradation products of dhvar1 and dhvar2 appeared within one hour in the supernatants of Streptococcus mutans and Staphylococcus aureus. In contrast, the variants dhvar3 and dhvar4 were more resistant to degradation under the same conditions. MALDI-TOF analyses identified cleavage of dhvar1 and dhvar2 at Glu(6). The N-terminal peptide part (1-6) of dhvar1 and 2 showed no bactericidal activity, while peptide fragment (7-14) showed a highly reduced bactericidal activity.

Histatin 5 and derivatives. Their localization and effects on the ultra-structural level.

Histatins, a family of cationic peptides present in saliva, are active against the opportunistic yeast Candida albicans. The mechanism of action is still unclear. Histatin 5 and more potent synthetic variants, dhvar4 and dhvar5, were used to study localization and effects on morphology on the ultra-structural level. Although all peptides induced leakage, no association with the plasma membrane, indicative for permanent pores, was observed with immuno-gold-labeling. Freeze-fracturing showed severe changes of the plasma membrane. Together with, for the dhvars, the loss of intracellular integrity, this suggests that leakage may be a secondary effect rather than an effect of formation of permanent pores.