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1.A.84.1.2
The human calcium homeostasis modulator protein 2, CALHM2 or FAM16B, of 323 aas and 4 or 5 TMSs. The structures and gating mechanism of CALHM2 have been reported (Choi et al. 2019). Cryo-EM structures in the Ca2+-free active or open state and in the ruthenium red (RUR)-bound inhibited state, have been solved at 2.7 Å resolution (see also Syrjanen et al. 2020 and Demura et al. 2020. Purified CALHM2 channels form both gap junctions and undecameric hemichannels. The protomer shows a mirrored arrangement of the TMSs (helices S1-S4) relative to other channels with a similar topology, such as connexins, innexins and volume-regulated anion channels. Upon binding to RUR, a contracted pore with notable conformational changes of the pore-lining helix S1 was observed, which swings nearly 60 degrees towards the pore axis from a vertical to a lifted position. Possibly a two-section gating mechanism is operative in which the S1 helix coarsely adjusts, and the N-terminal helix fine-tunes, the pore size (Choi et al. 2019). The Kilifish CALHM1 octameric structure reveals that the N-terminal helix forms the constriction site at the channel pore in the open state and modulates the ATP conductance. The CALHM2 undecamer and CLHM-1 nonamer structures show  different oligomeric stoichiometries among CALHM homologs. The cryo-EM structures of a chimeric construct revealed that the intersubunit interactions in the transmembrane region and the TMS-intracellular domain linker define the oligomeric stoichiometry (Demura et al. 2020).

Accession Number:Q9HA72
Protein Name:Calcium homeostasis modulator protein 2
Length:323
Molecular Weight:36175.00
Species:Homo sapiens (Human) [9606]
Number of TMSs:3
Location1 / Topology2 / Orientation3: Membrane1 / Multi-pass membrane protein2
Substrate Ca2+

Cross database links:

Structure:
6LMU   6LMW   6LMX   6UIV   6UIW   6UIX   6VAI   6VAK   6VAL      [...more]

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FASTA formatted sequence
1:	MAALIAENFR FLSLFFKSKD VMIFNGLVAL GTVGSQELFS VVAFHCPCSP ARNYLYGLAA 
61:	IGVPALVLFI IGIILNNHTW NLVAECQHRR TKNCSAAPTF LLLSSILGRA AVAPVTWSVI 
121:	SLLRGEAYVC ALSEFVDPSS LTAREEHFPS AHATEILARF PCKENPDNLS DFREEVSRRL 
181:	RYESQLFGWL LIGVVAILVF LTKCLKHYCS PLSYRQEAYW AQYRANEDQL FQRTAEVHSR 
241:	VLAANNVRRF FGFVALNKDD EELIANFPVE GTQPRPQWNA ITGVYLYREN QGLPLYSRLH 
301:	KWAQGLAGNG AAPDNVEMAL LPS