Isolation and evaluation of nonsiderophore cyclic peptides from marine sponges

The world's oceans are iron-deficient environments and there is little know ledge available regarding iron uptake by marine sponges. To understand iron -related biofunctions in marine organisms, iron-binding natural compounds f rom marine sponges were investigated. Here we reported a natural compound h aliclonamide A and its analogue haliclonamide B were isolated from the mari ne sponge Haliclona sp. and their structures were investigated by spectrosc opic analysis. The structure of haliclonamide A was determined to consist o f novel cyclic peptides containing oxazole and methyloxazoline rings. Mass spectra revealed that these two compounds formed a 1:1 stable complex with trivalent iron but not with divalent iron. EPR analysis showed that these c ompounds will bind with Fe(III) and Cr(III) specifically, but will not bind to other cation ions such as CU2+, Zn2+, CO2+, Ni2+, Al3+, and Ti3+. The b inding constant of compound-iron complex was 10(19) which is lower than the binding constant of siderophores. The Fe(III) concentration in this sponge tissue was shown to be 10 and 100 times higher than the other sponge tissu es and seawater. This indicated the sponge Haliclona sp. may possibly uptak e iron through nonsiderophore metal-binding peptides haliclonamides A and B . It also suggests that iron uptake activity of marine organisms may occur through nonsiderophore metal-binding peptides in natural ocean. (C) 2001 Ac ademic Press.