(a) A stereoview of the Cα trace of the PgaB N-terminal domain (PGABN), looking into the central barrel. The trace is coloured from blue (Pro43) to red (Val308), with α-helices shown as coils and β-strands as arrows. The figure was drawn using PyMOL (DeLano, 2002). Secondary structure was determined automatically. (b) The Cα trace of the PGABN monomer, coloured as in (a), is shown on the left, with the active-site zinc ion shown as a grey sphere. Residues coordinating the metal are shown as sticks, with O atoms coloured red and N atoms blue. The right-hand panel shows a surface representation of the monomer in the same orientation coloured by electrostatic potential. The zinc ion and acetate ligand were omitted from the calculation of the potential and are shown as ball-and-stick models over the protein surface. The strong negative charge of the active site is apparent. The remainder of the protein surface shows no distinct pattern of charge.