Purification, crystallization and preliminary X-ray diffraction analysis of the lytic transglycosylase MltF from Escherichia coli

The lytic transglycosylase MltF from Escherichia coli is an outer-membrane-bound periplasmic protein with two domains: a C-terminal catalytic domain with a lysozyme-like fold and an N-terminal domain of unknown function that is homologous to the periplasmic substrate-binding proteins of ABC transporters. In order to investigate its structure and function, a soluble form of full-length MltF (sMltF) containing both domains and a soluble fragment containing only the N-terminal domain (sMltF-NTD) were purified and crystallized. Crystals of sMltF belonged to space group P4(3)2(1)2 or P4(1)2(1)2, with unit-cell parameters a = b = 110.8, c = 163.5 angstrom and one or two molecules per asymmetric unit. A complete data set was collected to 3.5 angstrom resolution. Crystals of sMltF-NTD belonged to space group P3(1)21, with unit-cell parameters a = b = 82.4, c = 75.2 angstrom and one molecule per asymmetric unit. For sMltF-NTD, a complete native data set was collected to 2.20 angstrom resolution. In addition, for phasing purposes, a three-wavelength MAD data set was collected to 2.5 angstrom resolution using a bromide-soaked sMltF-NTD crystal. Using phases derived from the Br-MAD data, it was possible to build a partial model of sMltF-NTD.