Inhibition of bactericidal activity is maintained in a mouse alpha-defensin precursor with proregion truncations

alpha-Defensin biosynthesis requires the proteolytic conversion of inactive precursors to microbicidal forms. In mouse Paneth cell pro-alpha-defensin proCrp4((20-92)), anionic amino acids positioned near the proregion N-terminus inhibit proCrp4 activity by an apparent charge neutralization mechanism. Because most pro-alpha-defensins contain proregions of highly conserved chain length, we tested whether decreasing the distance between the inhibitory acidic residues of the proregion and the alpha-defensin component of the precursor would alter proCrp4 inhibition. Accordingly, two proCrp4 deletion variants, (Delta44-53)-proCrp4 and (Delta44-58)-proCrp4, truncated in a manner corresponding to deletions between MMP-7 cleavage sites, were prepared and assayed for bactericidal peptide activity. Consistent with the properties of full-length proCrp4((20-92)), (Delta44-53)-proCrp4 and (Delta44-58)-proCrp4 were processed effectively by MMP-7, lacked bactericidal activity at high peptide levels over a 3h exposure period, and failed to induce permeabilization of live Escherichia coliin vitro. Thus, bringing the inhibitory proregion domain into greater proximity with the Crp4 component of the precursor did not alter the activity of this pro-alpha-defensin. Therefore, the conserved distance that separates inhibitory acidic proregion residues from the Crp4 peptide is not critical to maintaining proCrp4((20-92)) in an inactive state.