Truncation of amidated fragment 33-61 of bovine alpha-hemoglobin: effects on the structure and anticandidal activity.

Peptides derived from endogenous hemoglobin play important biological roles in a variety of living systems. In previous works we showed that the fragment 33-61 of bovine alpha-hemoglobin (Hb33-61) and its C-terminus amidated analogue (Hb33-61a) exhibit antimicrobial activity and we determined the 3D structure of Hb33-61a bound to sodium dodecyl sulfate micelles. Here we report that Hb33-61a is lethal to Candida albicans at 6.25 microM probably through disruption of its plasma membrane. In addition, we show that, even when used at 50 microM, Hb33- 61a produces low hemolysis (16% +/- 3.0%). Recognizing that one of the key steps to study new compounds with potential pharmaceutical application is to identify the structural elements essential to express biological activity, we also investigated the anticandidal activity of Hb33- 61a fragments. The results indicated that Hb40-61a exhibits the same minimal inhibitory concentration as Hb33-61a, whereas Hb33-52a and Hb48-61a are significantly less active. Noteworthy, for all the peptides tested, we observed that C-terminus amidation produces a potentiation of their anticandidal activity and we associate that increased biological activity to a preferred structural and spatial organization of the C-terminal region favored by amidation. Finally, the data show that the most active peptides (Hb33-61a and Hb40-61a) are characterized by a central hinge joining the C-terminal region that presents, containing a beta-turn, followed by and a helical element, to the N-terminal region that presents only a beta-turn. We hypothesize that these two structured regions, by fluctuating independently in the lipid environment, may act in a coordinated fashion disrupting the yeast plasma membrane.