Structural features of the Pex5p-SCP2 ancillary interface. (A) Cartoon of the X-ray crystal structure of Pex5p(C) in complex with mSCP2 . Pex5p(C) is shown in green and mSCP2 in blue. A partial surface representation for mSCP2 is shown, denoting the residues of mSCP2 that approach Pex5p(C) to < 4 Å - that is, the extended C-terminal PTS1 buried within Pex5p(C) and the ancillary helix-helix interface. The ancillary interface is highlighted - residues contributed by mSCP2 are coloured in burgundy and those contributed by Pex5p(C) in yellow. (B) Amino acid sequence alignment of the C-terminal 3-helix segment of Pex5p, using the standard letter code. The following colour scheme is used: CFILMPVWY (green), HNQST (magenta), DE (red), KR (blue) and AG (yellow). The alignment was generated with CLUSTAL-W  and manually adjusted, the figure generated in ALINE . Positions of α-helices 15, 16 and 17 (from the human Pex5p(C)/mSCP2 crystal structure, PDB accession 2C0L, ) as defined by DSSP  are indicated at the top of the figure. Residues marked with an arrowhead (black triangle) were mutated in this study. Species identifiers: Tb, Trypanosoma brucei; Yl, Yarrowia lipolytica; At, Arabidopsis thaliana; Cl, Citrullus lanatus; Nt, Nicotiana tabacum; Br, Brachydanio rerio; Cg, Cricetulus griseus; Cp, Cavia porcellus; Hs, Homo sapiens; Mm, Mus musculus; Ce, Caenorhabditis elegans; Dm, Drosophila melanogaster; Pc, Penicillium crysogenum; Hp, Hansenula polymorpha; Pp, Pichia pastoris; Ld, Leishmania donovani; Nc, Neurospora crassa; Rn, Rattus novegicus; Sc, Saccharomyces cerevisiae; Sp, Schizosaccharomyces pombe. The human Pex5p sequence is indicated with an asterisk (black star). In mammalian sequences, (L) and (S) denote whether the numbering used refers to the long or short forms of Pex5p. (C) Stereo view focusing on the ancillary interface between Pex5p(C) and mSCP2 . The protein colour scheme is as in (A). Sidechains are shown for residues at the interface. See text for details. (D) View showing the different arrangement of key Pex5p residues at the ancillary interface in the presence (green) and absence (red) of mSCP2 . See text for details. Crystal structure figures were prepared in PyMOL (http://www.pymol.org).