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 P 4 3 2 1 2 or P 4 1 2 1 2, with unit‐cell parameters a  =  b  = 110.8, c  = 163.5 Å and one or two molecules per asymmetric unit. A complete data set was collected to 3.5 Å resolution. Crystals of sMltF‐NTD belonged to space group P 3 1 21, with unit‐cell parameters a = b = 82.4, c = 75.2 Å and one molecule per asymmetric unit. For sMltF‐NTD, a complete native data set was collected to 2.20 Å resolution. In addition, for phasing purposes, a three‐wavelength MAD data set was collected to 2.5 Å 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.