A mixture of α-helical and 310-helical conformations for involucrin in the human epidermal corneocyte envelope provides a scaffold for the attachment of both lipids and proteins

Abstract

Involucrin plays an important role in the lipid and protein compound envelopes of mammalian epidermal corneocytes. In the present study, model peptides containing the consensus repeating units PEQQEGQLEL and LEQQEGQLEH, found in the central region of human involucrin, were studied by circular dichroism spectroscopy, molecular modeling, and energy minimization. These peptides have intrinsic α-helix-forming properties as indicated by their circular dichroic spectra obtained in the presence of 2,2,2-trifluoroethanol. Peptide (LEQQEGQLEH)3 had an α-helix content of 100% in 100% 2,2,2- trifluoroethanol at 0 °C. The energy-minimized α-helix showed that only 50% of the glutamate side chains may be available for the attachment of lipids. However, when a 310-helix was assumed for the GQL or GQLE residues in LEQQEGQLEH, all of the glutamate side chains were arrayed on one face of the helix, and all of the glutamine side chains were arrayed on the opposite face. A similar result was obtained when the nonhelical part of PEQQEGQLEL was assumed to contain a β-turn III, which is equivalent to a short portion of 310-helix. The results of this study suggest that when the central segment of human involucrin is predominantly α-helical, accompanied by short 310-helical segments, the protein can function as a scaffold for the attachment of both lipids and proteins.