The protease domains of the meprin metalloproteinase and subunits are 55% identical in amino acid sequence yet they have very different peptide bond specificities. The cover illustration shows two views of the three-dimensional structures of the meprin subunits and highlights the charge differences that provide insight into the distinct substrate preferences. The blue, red, and yellow colors indicate basic, acidic, and catalytic center residues, respectively. S and S' are the putative substrate binding regions. Details can be found in the article by Bertenshaw et al., pages 13248-13255.13248.