1.A.87.1.1
Plant Ca²⁺ channel protein, Mid1 complementary activity 1, MCA1 (Iida et al. 2013).  MCA1 and MCA2 each forms a homotetramer and exhibit Ca²⁺-permeable mechanosensitive channel activity.  Both are single-pass type I transmembrane proteins with their N-termini located extracellularly and their C-termini located intracellularly. An EF hand-like motif, coiled-coil motif, and Plac8 motif may all be in the cytoplasm, suggesting that the activities of both channels can be regulated by intracellular Ca²⁺ and protein interactions (Kamano et al. 2015). However, hydropathy plots suggest that the Plac8 domain may be transmembrane with 3 TMSs.  mca1 but not mca2 mutants show defects in root entry into hard agar, whereas mca2 but not mca1 mutants are defective in Ca²⁺ uptake in A. thaliana roots (Hamilton et al. 2015). Root growth reduction in response to mechanical stress involves MCA1 tgether with WDL5 (Q94C48) subject to ethylene-mediated regulation) and the co-receptor BAK1 (Q94F62) (Okamoto et al. 2021).