Delineation of a membrane-proximal beta-rich domain in the GABA(A) receptor by progressive deletions

The type A gamma-aminobutyric acid (GABA,) receptor plays a major inhibitor y role in the central nervous system. Structural elucidation of the GABA, r eceptor has been impeded by the large size of the receptor. We present here the delineation of a minimal structural domain as the first step of dissec ting the receptor structure. This was achieved through prediction-assisted progressive deletions: the prediction of a candidate structural domain rich in beta-strands with no close similarity to known structures was tested by deleting putative secondary structure elements from the ends of the propos ed domain, as well as mutations within the terminal secondary structures. S uch progressive deletions revealed the limits of an integral domain, spanni ng Cysl80 to Met293 (numbering of human alpha 1 subunit). Below these limit s the intact domain structure, as indicated by its circular dichroism, coll apses. Based on its putative position, this domain is provisionally designa ted the membrane-proximal beta-rich domain of GABA(A) receptor. The inclusi on of sequences from the first two out of four previously suggested transme mbrane segments and one of the two conserved Cys residues in this domain de fines important constraints to the receptor structure. (C) 1999 Academic Pr ess.