Aspergillus nidulans BapH is a RAB11 effector that connects membranes in the Spitzenkörper with basal autophagy.

Abstract

Using affinity chromatography we identified the Aspergillus nidulans F-BAR-and-PH domain-containing protein BapH as a RabERAB11 effector. BapH localizes to the Spitzenkörper (SPK) in an F-actin- and Sec7-dependent manner, becoming cytosolic after inactivation of Trs120 in TRAPPII, the oligomeric GEF for RabERAB11 . Therefore, RabERAB11 contributes to the recruitment of BapH to secretory vesicles in vivo. BapH has a close homologue, SlmA, which is related to yeast Slm1p/Slm2p, localizes to eisosomes and does not bind RabERAB11 . bapHΔ, slmAΔ and double bapHΔ slmAΔ mutations do not affect growth, although slmAΔ results in myriocin hypersensitivity. Both the PH and the F-BAR domain in BapH are necessary to recruit the protein to membranes, whereas its C-terminal moiety negatively regulates localization to the SPK. Strong overexpression of full-length BapH or of BapH lacking the C-terminal moiety impairs growth. The tandemly duplicated PHBapH domain is recruited to the plasma membrane in a manner dependent on critical Lys residues in its 'noncanonical' lipid binding pocket, suggesting that it binds to biological membranes containing PtdIns(4,5)P2 . Ablation of BapH, or deletion of the PH or BAR domains critical for the SPK localization increases autophagy under nitrogen-replete conditions. Therefore, BapH localizing to SPK vesicles influences basal levels of autophagy.