The crystal structure of human alpha-defensin HNP-3 revealed that it forms a dimer containing a six-stranded beta-sheet region (Hill et al. 1991). NMR studies indicate that HNP-1 can also form dimers or higher-order aggregates in solution and artificial lipid bilayers (Zhang et al. 1992, 2010a, 2010b). Models of alpha and beta defensins suggest that dimerization and/or higher order structures are characteristic, though not univeral or required for the biological effects of some beta-defensins (Suresh & Verma 2006, Pazgier et al. 2006).