Beta-defensin 2 (BD-2) also known as skin-antimicrobial peptide 1 (SAP1) is a peptide that in humans is encoded by the DEFB4 (defensin, beta 4) gene.

Human beta-defensin-2 (hBD-2) is a cysteine-rich cationic low molecular weight antimicrobial peptide discovered in lesional skin.

Structure

hBD-2 is a protein whose primary structure is made by 64 aminoacids. At concentrations <=2.4 mM, hBD-2 is monomeric. The structure is amphiphilic with a nonuniform surface distribution of positive charge and contains several key structural elements, including a triple-stranded, antiparallel beta sheet with strands 2 and 3 in a beta hairpin conformation. The determination of other structural elements depends on the technique used. When X-ray crystallography is used an alpha helix can be observed at the N-terminal end of the protein (PDB codes: ,, and ). When using NMR this alpha-helix does not appear (PDB code: ), however this structure was determined using a truncated version of hBD-2 which was missing the initial 4 amino acids, and may be the reason for the discrepancy.

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