This highly divergent repeat occurs in number of proteins implicated in cell aggregation [1]. The Pfam alignment probably contains three such repeats (personal obs: C Yeats). These are likely to have a beta-helical structure.

1: Filamentous hemagglutinin of Bordetella pertussis: nucleotide sequence and crucial role in adherence. Relman DA, Domenighini M, Tuomanen E, Rappuoli R, Falkow S; Proc Natl Acad Sci U S A 1989;86:2637-2641. PMID:2539596

2: Beta-helix model for the filamentous haemagglutinin adhesin of Bordetella pertussis and related bacterial secretory proteins. Kajava AV, Cheng N, Cleaver R, Kessel M, Simon MN, Willery E, Jacob-Dubuisson F, Locht C, Steven AC; Mol Microbiol 2001;42:279-292. PMID:11703654