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Title: The carboxyl-terminus of cytochrome b5 confers endoplasmic reticulum specificity by preventing spontaneous insertion into membranes

Author
item HENDERSON, MATTHEW - MCMASTER UNIVERSITY
item ANDREWS, DAVID - McMaster University
item HWANG, YEEN - University Of Guelph
item MULLEN, ROBERT - University Of Guelph
item Dyer, John

Submitted to: Biochemistry and Cell Biology
Publication Type: Abstract Only
Publication Acceptance Date: 12/1/2006
Publication Date: 12/1/2006
Citation: Henderson, M.P., Andrews, D.W., Hwang, Y.T., Mullen, R.T., Dyer, J.M. 2006. The carboxyl-terminus of cytochrome b5 confers endoplasmic reticulum specificity by preventing spontaneous insertion into membranes (abstract). Biochemistry and Cell Biology 84(6):1084-1084.

Interpretive Summary:

Technical Abstract: The molecular mechanisms that determine the correct subcellular localization of proteins targeted to membranes by tail-anchor sequences are poorly defined. Previously, we showed that two isoforms of tung tree (Vernicia fordii) tail-anchored cytochrome b5 (Cb5) target specifically to endoplasmic reticulum (ER)membranes both in vivo and in vitro (Hwang, Pelitre, Henderson, Andrews, Mullen, 2004. Plant Cell. 16:3002-3019). Here we examine the targeting of various tung Cb5 fusion proteins and truncation mutants to purified intracellular membranes in vitro in order to assess the importance of the charged carboxyl-terminal sequence in targeting to specific membranes. Removal of the carboxyl-terminal sequence from tung Cb5 proteins resulted in efficient binding to both ER and mitochondria. Results from organelle competition, liposome-binding and membrane proteolysis experiments demonstrated that removal of the carboxyl-terminal sequence results in spontaneous insertion of tung Cb5 proteins into lipid bilayers. Our results indicate that the carboxyl-terminal sequences from plant Cb5 proteins provide ER specificity by preventing spontaneous insertion into incorrect subcellular membranes.