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 C-terminal end of the protein (PDB code: 1fd3). When using NMR this alpha-helix does not appear (PDB code: 1e4q).
Defensins form a family of microbicidal and cytotoxic peptides made by neutrophils. Members of the defensin family are highly similar in protein sequence. Beta-defensin 2 is an antibiotic peptide which is locally regulated by inflammation.
Human beta-defensin 2 is produced by a number of epithelial cells and exhibits potent antimicrobial activity against Gram-negative bacteria and Candida, but not Gram-positive S. aureus. It has been speculated that beta-defensin 2 may contribute to the infrequency of Gram-negative infections on skin and lung tissue.
hBD-2 represents the first human defensin that is produced following stimulation of epithelial cells by contact with microorganisms such as P. aeruginosa or cytokines such as TNF-alpha and IL-1 beta. The HBD-2 gene and protein are locally expressed in keratinocytes associated with inflammatory skin lesions. It is intriguing to speculate that HBD-2 is a dynamic component of the local epithelial defense system of the skin and respiratory tract having a role to protect surfaces from infection, and providing a possible reason why skin and lung infections with Gram-negative bacteria are rather rare.
Although this protein doesn’t have any antibacterial activity against Gram-positive bacteria, there is a study showing that there is a synergy between hBD-2 and other proteins. One example of this synergistic effect is with epiP, a protein segregated by some strains of S. epidermidis. hBD2, holding hands with epiP, is capable of killing S. aureus, a Gram-positive bacteria responsible of human diseases.
Liu L, Wang L, Jia HP, et al. (1999). "Structure and mapping of the human beta-defensin HBD-2 gene and its expression at sites of inflammation.". Gene. 222 (2): 237–44. doi:10.1016/S0378-1119(98)00480-6. PMID9831658.
Yang D, Chertov O, Bykovskaia SN, et al. (1999). "Beta-defensins: linking innate and adaptive immunity through dendritic and T cell CCR6.". Science. 286 (5439): 525–8. doi:10.1126/science.286.5439.525. PMID10521347.
Harder J, Meyer-Hoffert U, Teran LM, et al. (2000). "Mucoid Pseudomonas aeruginosa, TNF-alpha, and IL-1beta, but not IL-6, induce human beta-defensin-2 in respiratory epithelia.". Am. J. Respir. Cell Mol. Biol. 22 (6): 714–21. doi:10.1165/ajrcmb.22.6.4023. PMID10837369.
Hoover DM, Rajashankar KR, Blumenthal R, et al. (2000). "The structure of human beta-defensin-2 shows evidence of higher order oligomerization.". J. Biol. Chem. 275 (42): 32911–8. doi:10.1074/jbc.M006098200. PMID10906336.
Ali RS, Falconer A, Ikram M, et al. (2001). "Expression of the peptide antibiotics human beta defensin-1 and human beta defensin-2 in normal human skin.". J. Invest. Dermatol. 117 (1): 106–11. doi:10.1046/j.0022-202x.2001.01401.x. PMID11442756.
Carothers DG, Graham SM, Jia HP, et al. (2001). "Production of beta-defensin antimicrobial peptides by maxillary sinus mucosa.". American journal of rhinology. 15 (3): 175–9. doi:10.2500/105065801779954238. PMID11453504.
Biragyn A, Surenhu M, Yang D, et al. (2002). "Mediators of innate immunity that target immature, but not mature, dendritic cells induce antitumor immunity when genetically fused with nonimmunogenic tumor antigens.". J. Immunol. 167 (11): 6644–53. doi:10.4049/jimmunol.167.11.6644. PMID11714836.
Takahashi A, Wada A, Ogushi K, et al. (2001). "Production of beta-defensin-2 by human colonic epithelial cells induced by Salmonella enteritidis flagella filament structural protein.". FEBS Lett. 508 (3): 484–8. doi:10.1016/S0014-5793(01)03088-5. PMID11728477.
Schibli DJ, Hunter HN, Aseyev V, et al. (2002). "The solution structures of the human beta-defensins lead to a better understanding of the potent bactericidal activity of HBD3 against Staphylococcus aureus.". J. Biol. Chem. 277 (10): 8279–89. doi:10.1074/jbc.M108830200. PMID11741980.