Research

Membrane-bound progesterone receptors contain a cytochrome b₅-like ligand-binding domain

William Mifsud^1,2 and Alex Bateman¹

¹The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton CB10 1SA, UK

²University of Malta Medical School, Saint Luke's Hospital, Guardamangia Hill, Guardamangia MSD 09, Malta

author email corresponding author email

Genome Biology 2002, 3:research0068.1-0068.5doi:10.1186/gb-2002-3-12-research0068

Published:	12 November 2002

Subject areas: Biochemistry and structural biology, Physiology, Evolution

Abstract

Background

Membrane-associated progesterone receptors (MAPRs) are thought to mediate a number of rapid cellular effects not involving changes in gene expression. They do not show sequence similarity to any of the classical steroid receptors. We were interested in identifying distant homologs of MAPR better to understand their biological roles.

Results

We have identified MAPRs as distant homologs of cytochrome b₅. We have also found regions homologous to cytochrome b₅ in the mammalian HERC2 ubiquitin transferase proteins and a number of fungal chitin synthases.

Conclusions

In view of these findings, we propose that the heme-binding cytochrome b₅ domain served as a template for the evolution of membrane-associated binding pockets for non-heme ligands.