Cryo-EM Structure and Function of the Human BEST1 Channel Complexed with a Metabolic Enzyme

초록

Bestrophin (BEST) channels are calcium-activated chloride (Cl⁻) channels that respond to increases in cytoplasmic [Ca²⁺]. The human genome has four paralogs (BEST1–BEST4), sharing ~60% sequence identity in the N-terminal but only 6–19% in the C-terminal region. Significant sequence differences also exist among BEST1 orthologs. Our recent research suggested that the marginally conserved C-terminal region regulates calcium sensitivity, expression, and membrane targeting in both human and mouse BEST1. To gain an insight for understanding functional differences in the Best1 orthologs, we used IP-MS to identify proteins interacting with hBEST1’s C-terminal region and found PYCR3, an enzyme involved in proline metabolism, as a binding partner. This interaction was confirmed via Co-IP and SEC. The hBEST1-PYCR3 complex structure (~3 Å) shows PYCR3 as a decamer attached to hBEST1’s pentamer. The transmembrane domain of hBEST1 rotates, suggesting PYCR3 may facilitate channel opening. Co-expression of PYCR3 increased hBEST1 current density, while PYCR3 knockdown reduced it. We are currently exploring the mechanism of PYCR3-dependnet hBEST1 channel modulation.