Characterizing the membrane recruitment domain of BDCPs and its role in gray platelet syndrome.

BEACH domain-containing proteins (BDCPs) represent a family of large membrane-associated transmembrane cargo adaptors. In the current study, we determined the cryo-EM structure of the full-length typical BDCP NBEAL2, revealing an N-terminal arch-like structure with C-terminal globular domains attached to its convex surface. Using structure-guided deletion mutants and protein chimeras as well as native alternatively spliced isoforms and disease-related point mutants, we show that the N-terminal α-solenoid/concanavalin A-like domain assembly of the typical BDCPs NBEAL1, NBEAL2, LYST, ALFY, LRBA, and NBEA functions as a modular membrane recruitment domain. We report that gray platelet syndrome-associated single aa mutations L388P or E643V within the membrane recruitment domain of NBEAL2 disrupt its membrane targeting in stably transfected cells, highlighting a potential structure-function mechanism by which failed membrane recruitment cause gray platelet syndrome or other BDCPs-related diseases.