Candidacidal activity of recombinant human salivary histatin-5 and variants.
Human salivary histatins possess fungicidal and bactericidal activities. The current investigation evaluates the structure-function relationship of histatins with regard to their candidacidal activity by using recombinant histatin-5 and its variants produced in Escherichia coli. The purified recombinant histatins were examined for their candidacidal activity and secondary structure. The m21 (with Lys-13 replaced by Thr [Lys-13-->Thr]) and m71 (Lys-13-->Glu) variants are significantly less effective than recombinant histatin-5 in killing Candida albicans, suggesting that Lys-13 is critical for candidacidal activity. The m68 (Lys-13-->Glu and Arg-22-->Gly) variant is significantly less potent than the recombinant histatin-5 as well as m71, indicating that Arg-22 is crucial for the cidal activity. The candidacidal activities of m1 (Arg-12-->Ile), m2 (Arg-12-->Ile and Lys-17-->Asp), m12 (Arg-12-->Lys and His-21-->Leu), and m70 (His-19-->Pro and His-21-->Arg) variants, however, are comparable to that of recombinant histatin-5, indicating that Arg-12, Lys-17, His-19, and His-21 are not functionally important. The conformational preferences of histatin-5 and variants were determined by circular dichroism. The results indicate that all proteins have a strong tendency to adopt alpha-helical conformation in trifluoroethanol. Previously, we have shown that the alpha-helical conformation is one of the important structural requirements for eliciting appreciable candidacidal activity. Collectively, the data suggest that in addition to the helical conformation, specific residues such as Lys-13 and Arg-22 in the sequence of histatin-5 are, indeed, important for candidacidal activity.
Tsai
H
H
Department of Oral Biology, School of Dental Medicine, State University of New York at Buffalo, 14214, USA.
Raj
P A
PA
Bobek
L A
LA
D000595:Amino Acid Sequence; D000935:Antifungal Agents / Q000494:pharmacology; D004926:Escherichia coli / Q000235:genetics; D054808:Histatins; D006801:Humans; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000235:genetics / Q000494:pharmacology; D012471:Salivary Proteins and Peptides / Q000235:genetics* / Q000494:pharmacology; D013329:Structure-Activity Relationship
D000935:Antifungal Agents; C068075:HTN3 protein, human; D054808:Histatins; D011994:Recombinant Proteins; D012471:Salivary Proteins and Peptides