This domain is found in proteins from nematodes, including SXP/RAL-2 family protein Ani s 5 (ANIS5) from Anisakis simplex, and comprises two conserved motifs: SXP1 and SXP2 [1]. Although the function of this domain is not clear, structural information from ANIS5 revealed an alpha helical arrangement with a Calmodulin-like fold. Functional studies indicates that ANIS5 can bind magnesium and calcium, suggesting that this domain plays a role in cation binding [2]. These proteins are interesting targets to develop control strategies against the diseases caused by parasites.

1: Relationships between IgE/IgG4 epitopes, structure and function in Anisakis simplex Ani s 5, a member of the SXP/RAL-2 protein family. Garcia-Mayoral MF, Trevino MA, Perez-Pinar T, Caballero ML, Knaute T, Umpierrez A, Bruix M, Rodriguez-Perez R; PLoS Negl Trop Dis. 2014;8:e2735. PMID:24603892

2: Identification and Physicochemical Characterization of a New Allergen from Ascaris lumbricoides. Ahumada V, Manotas M, Zakzuk J, Aglas L, Coronado S, Briza P, Lackner P, Regino R, Araujo G, Ferreira F, Caraballo L; Int J Mol Sci. 2020; [Epub ahead of print] PMID:33371317