Figure 5. Evidence from multiple sequence alignments that PBD1 and PBD2 are unusual hybrid PtdIns(3,4,5)P₃-binding domains.

(A) Previous molecular modelling studies [10] have identified residues 530–1047 as a phosphatase-like region of Vip1 from Saccharomyces cerevisiae (scVip); the N-terminus of this domain was aligned (using ClustalX) with corresponding residues in the PBDs of PPIP5K1 (residues 382–453), PPIP5K2 (residues 371–442), hMIPP and the E. col. phytase. The RHGXRXP acid-phosphatase motif in the PBDs is boxed. The bar graph (generated with ClustalX 2.0.10) shows the conservation score (on a scale of 0 to 100 %) for each residue in the alignment. (B) A separate ClustalX sequence alignment of PBD1, PBD2 and several PtdIns(3,4,5)P₃ -specific PH domains (GRP-1, PHLDB1 and PSCD3 are from mice; DAPP1, PLEKHA1, AKT1 and BTK are human sequences). The arrows mark two conserved basic residues in PBD1 (Arg³⁹⁹ and Arg⁴¹⁷) that were selected for mutagenesis studies. Other conserved amino acid residues that are identical or similar in nature have also been highlighted. GenBank^® accession numbers: scVip1, NP_013514; hMIPP, AAH32504.1; Phytase, 9954897; PBD2, NP_056031.2; PBD1, AAH57395.1; GRP-1, AAB60876.1; PSCD3, EDL19040.1; DAPP1, AAH12924.1; PLEKHA1, AAH01136.1; AKT1, AAL55732.1; PHLDB1, AAH69853.1; BTK, NP_000052.1.