The solution structure of an N-terminally truncated version of the yeast CDC24p PB1 domain shows a different β-sheet topology

Phox and Bem1 (PB1) domains mediate protein–protein interactions via the formation of homo- or hetero-dimers. The C-terminal PB1 domain of yeast cell division cycle 24 (CDC24p), a guanine-nucleotide exchange factor involved in cell polarity establishment, is known to interact with the PB1 domain occurring in bud emergence MSB1 interacting 1 (BEM1p) during the regulation of the yeast budding process via its OPR/PC/AID (OPCA) motif. Here, we present the structure of an N-terminally truncated version of the Sc CDC24p PB1 domain. It shows a different topology of the β-sheet than the long form. However, the C-terminal part of the structure shows the conserved PB1 domain features including the OPCA motif with a slight rearrangement of helix α1. Residues which are important for the heterodimerization with BEM1p are structurally preserved.