MCAfunc domain (MCAfunc) is located in the N-terminal region of a mechanosensitive channel protein MID1-COMPLEMENTING ACTIVITY (MCA). MCAfunc represents the provisionally advocated ARPK domain (Amino-terminal domain of Rice putative Protein Kinases), overlapping with the EF hand-like region at the N-terminus [1]. In MCA proteins, MCAfunc has Ca2+ influx activity and is proposed to be a functional domain of MCAs [2]. MCAfunc is exclusively observed in streptophytes and exists not only in MCA but also in E3 ubiquitin ligase-like proteins, ARO3 like proteins and and protein kinases. In the most basal plant lineage, charophytes, MCAfunc is only found in E3 ubiquitin ligase-like proteins and protein of presently unknown function, while MCA proteins are exclusively found in land plants, from bryophytes to angiosperms [3].

1: Arabidopsis plasma membrane protein crucial for Ca2+ influx and touch sensing in roots. Nakagawa Y, Katagiri T, Shinozaki K, Qi Z, Tatsumi H, Furuichi T, Kishigami A, Sokabe M, Kojima I, Sato S, Kato T, Tabata S, Iida K, Terashima A, Nakano M, Ikeda M, Yamanaka T, Iida H; Proc Natl Acad Sci U S A. 2007;104:3639-3644. PMID:17360695

2: Determination of structural regions important for Ca(2+) uptake activity in Arabidopsis MCA1 and MCA2 expressed in yeast. Nakano M, Iida K, Nyunoya H, Iida H; Plant Cell Physiol. 2011;52:1915-1930. PMID:21949028

3: Mix and match: Patchwork domain evolution of the land plant-specific Ca2+-permeable mechanosensitive channel MCA. Nishii K, Moller M, Iida H; PLoS One. 2021;16:e0249735. PMID:33857196