Location of tolerated insertions/deletions in the structure of the maltose binding protein

In a previous study [(1987) J. Mol. Biol. 194, 663-673], we isolated ten insertion/deletion mutants (indels) of the maltose binding protein for which the maltose binding constant was only a little or not at all affected. In this paper, we have localized these mutations in the recently solved three-dimensional structure. Contrary to the general expectation, most of the insertion/deletion modifications occurred within elements of secondary structure. An analysis of the inserted residues for three indels found within alpha helices allowed an interpretation regarding protein structure accommodation to such modifications.