Protein Targeting

Assembly and Function of the SRP Receptor

The SRP receptor is the site on the endoplasmic reticulum of targeting of ribosomes bound by SRP.   These ribosomes are  synthesizing secreted and integral membrane proteins.

The eukaryotic SRP receptor is composed of two subunits called SR a and SR b.

In E. coli the homologue of the SRP receptor is FtsY

Recent Research

We discovered that the SR a subunit is assembled on the endoplasmic reticulum by binding to the SRb subunit during an mRNA encoded pause in translation (Young and Andrews, EMBOJ. 1996). 

Both our lab and that of Peter Walter have shown that SRb is a conventional type I transmembrane protein that requires SRP and SRP receptor to assemble into the endoplasmic reticulum membrane (Young et al. JBC, 1995).  

Both subunits of the SRP receptor are GTPases. SRa binds to the GTP bound form of SRb suggesting a novel way in which SRb contributes to protein targeting.(Legate and Andrews, Biochem Cell Biol. 2001) 

FtsY (which is strictly speaking the homologue of only SRa) binds directly to E. coli membranes by binding to  phosphatid-thanolamine.  Although there is no homologue for SRb in the E. coli genome, we have very good evidence that FtsY binds to a protein in the E. coli membrane. (Millman et al. JBC, 2001)

SRb is a unique GTP binding protein in that it has no intrinsic GTP activity. (Legate and Andrews, JBC, 2003)

Current Research

Novel functions for FtsY

FtsY Proteomics

Membrane binding by Sec61b and Sec61g.

Membrane targeting and function of Sec61g in yeast Sss1p