CRYSTALLIZATION OF A SOLUBLE, CATALYTICALLY ACTIVE FORM OF ESCHERICHIA-COLI LEADER PEPTIDASE

Leader peptidase, a novel serine protease in Escherichia coli, catalyz es the cleavage of the amino-terminal leader sequences from exported p roteins. It is an integral membrane protein containing two transmembra ne segments with its carboxy-terminal catalytic domain residing in the periplasmic space. Here, we report a procedure for the purification a nd the crystallization of a soluble non-membrane-bound form of leader peptidase (Delta 2-75). Crystals were obtained by the sitting-drop vap or diffusion technique using ammonium dihydrogen phosphate as the prec ipitant, Interestingly, we have found that the presence of the deterge nt Triton X-100 is required to obtain crystals sufficiently large for X-ray analysis, The crystals belong to the tetragonal space group P4(2 )2(1)2(1) with unit cell dimensions of a = b = 115 Angstrom and c = 10 0 Angstrom, and contain 2 molecules per asymmetric unit. This is the f irst report of the crystallization of a leader (or signal) peptidase. (C) 1995 Wiley-Liss, Inc.