Analyzing the Functions and Structure of the Human Lipodystrophy Protein Seipin.

Disruption of the gene BSCL2, which encodes the protein seipin, causes severe generalized lipodystrophy in humans with a near complete absence of adipose tissue. Moreover, cell culture studies have demonstrated that seipin plays a critical cell-autonomous role in adipocyte differentiation. These observations reveal seipin as a critical regulator of human adipose tissue development; however, until recently very little has been known about the potential molecular functions of this intriguing protein. Despite significant recent interest in the function of seipin, our understanding of its molecular role(s) remains limited. The topology of seipin and lack of evidence for any enzymatic domains or activity indicate that it may act principally as a scaffold for other proteins or play a structural role in altering membrane curvature and/or budding. Work in this area has been hampered by several factors, including the lack of homology that might imply testable functions, the poor availability of antibodies to the endogenous protein and the observation that this hydrophobic ER membrane-resident protein is difficult to analyze by standard Western blotting techniques. Here we summarize some of the techniques we have applied to investigate the association of seipin with a recently identified binding partner, lipin 1. In addition, we describe the use of atomic force microscopy (AFM) to image oligomers of the seipin protein. We believe that AFM will offer a valuable tool to examine the association of candidate binding proteins with the seipin oligomer.