designing site-specific protease sites

[Gregg B. Wells]

What proteases can be used for very specific cleavage of designed 
cleavage sites in recombinant proteins?  I know that thrombin, 
enterokinase, and factor X sites have been used in expression vectors to 
separate fusion proteins and to remove histidine tags.  What conditions 
optimize the chances for site-specific proteolysis?  Are any other 
enzymes used for this purpose?  I am particularly interested in cleaving 
a recombinant protein very near a membrane surface.  Are
any proteases especially good at working in this environment?
Thanks for the help.

Gregg Wells
Department of Pathology
University of Pennsylvania
Philadelphia, Pennsylvania
USA
email:  pathology at a1.mscf.upenn.edu