The BEACH domain is common for a protein family that has expanded through eukaryotic evolution and contains eight human proteins. These proteins are generally very large and at their C-terminal ends contain a conserved set of domains, a PH-like domain directly followed by a BEACH domain and a WD40 domain. Outside the recognized C-terminal domains, the rest of the proteins are weakly conserved and few functional domains have been recognized. According to their phylogenetic relationship they can be divided into four subfamilies with two closely related proteins in each. ALFY and WDFY4 make up one of these subfamilies where ALFY has been shown to be involved in degradation of protein aggregates, suggesting misregulation of ALFY
might contribute to neurodegeneration. NBEAL1 and NBEAL2 form another closely related pair and little is known about these proteins, but recently mutations in NBEAL2 was shown to be causative for the bleeding disorder grey platelets syndrome. LRBA and NBEA are the most
studied BEACH proteins and whereas LRBA is implicated in cancers of various types, NBEA is essential for neuromuscular transmission and correlated to autism. LYST and FAN form the final subclass of BEACH proteins. FAN is exceptional in being much smaller than the others, and LYST is well known because mutations in this protein causes Chediak-Higashi syndrome. In summary, the eight BEACH proteins are correlated to a varied set of diseases and studies of their cellular functions so far suggests they have little in common, although some BEACH proteins have been poorly studied. The BEACH domain is highly conserved through the protein family, but the function of the domain is not known.
For ALFY, a region of the protein containing the PH-like and BEACH domains has been shown to interact with the ubiquitin-binding protein p62. p62 associates with misfolded and mutant aggregating proteins to aid in their controlled aggregation to form ubiquitinated p62 bodies, which can be targeted for degradation in the acidic interior of the lysosome. Lysosomal degradation in this case starts with de novo formation of a double-membrane structure that surrounds p62 bodies,
sequestering them from the rest of the cell and eventually fusing with a lysosome where they are exposed to degrading hydrolases. This process is called macroautophagy and ALFY is linked to this process by its interaction with p62, but also by interacting with other components of the autophagic machinery through its WD40 and FYVE domains. Through this project we have found that the PH-BEACH domains of several BEACH proteins co-localize and interact directly with p62. The results indicate that BEACH proteins of all subfamilies interact with p62 through a groove formed between the PH-like and BEACH domains where residues from both domains seem to contribute to the interaction. Furthermore, autophagy assays were performed to study a
possible role for the BEACH proteins in autophagy. Knockdown of the proteins seems to not influence the rate of starvation-induced autophagy, but might influence the turnover of p62 under conditions of basal selective autophagy. Another screen for involvement in autophagy was performed by investigating localization of endogenous BEACH proteins in cell culture upon autophagy-promoting stressors. The results showed that puromycin-induced aggregation of misfolded proteins causes a clear recruitment of several of the BEACH proteins to the p62 bodies, indicating that similar to ALFY, other BEACH proteins may play a role as scaffolding proteins involved in selective autophagy.