1. Volume 6, Issue 12, Pages 1553-1561 (December 1998)
The crystal structure of pneumococcal surface antigen PsaA reveals a metal-binding site and a novel structure for a putative ABC-type binding protein 
Michael C Lawrence, Patricia A Pilling, V Chandana Epa, Anne M Berry, A David Ogunniyi, James C Paton 
Structure 
Volume 6, Issue 12, Pages (December 1998)
DOI: /S (98)

2. Figure 1
The overall fold of PsaA. (a) View down the twofold pseudosymmetry axis relating the domains. Within each domain, β strands are shown in cyan and α helices in brown; the domain-connecting helix is colored magenta. The connecting loops within the N-terminal domain are in yellow, whilst those in the C-terminal domain are colored green. The four metal-coordinating residues are shown in ball-and-stick representation, with carbon atoms colored gray, nitrogen atoms blue and oxygen atoms red. The Zn2+ is shown in orange. (b) Stereogram of a Cα trace of PsaA. The β strands are designated A–H and domain α helices a–h; the location of the Zn2+ (orange) is also shown. The N and C termini are shown as a blue and a red sphere, respectively, the observed N terminus being Lys24. Every twentieth Cα atom is highlighted as a black sphere and labeled. The view direction is approximately orthogonal to that of (a). Figures were generated using the programs MOLSCRIPT [39] and RASTER3D [40,41].
Structure 1998 6, DOI: ( /S (98) )

3. Figure 2
An alignment of sequences from Cluster 9 ABC-type binding proteins showing the relative locations of the PsaA secondary structural units and metal-binding site. The PsaA secondary structural elements are colored and labeled according to the scheme of Figure 1. Each subcluster I–VI is represented by a single member protein sequence and labeled accordingly (see Discussion section for definitions of subclusters and protein nomenclature). The numbering above the alignment is that of PsaA. Residues that are totally conserved within each subcluster are highlighted in green, and residues corresponding to the four primary PsaA metal-binding residues are highlighted in red; these are totally conserved within each subcluster. Trp141 and the first two residues of the DPH motifs are highlighted in yellow when totally conserved within each subcluster. The strand-bridging residue Glu254 is highlighted in blue when conserved within each subcluster. The LXXC lipoprotein motif is boxed in sequences from Gram-positive organisms. The sequence shown for PsaA is that of S. pneumoniae serotype 2 strain D39 [2], which, following this work, is now considered identical to that of serotype 6B strain SP-86 (JCP, unpublished results). The sequence of S. pneumoniae AdcA includes the correction Ile 138 to His (JP Claverys, personal communication). Sequence alignment was performed using the program CLUSTALW [42] followed by some manual editing. The Figure was produced using the program ALSCRIPT 2.04 [43].
Structure 1998 6, DOI: ( /S (98) )

4. Figure 3
The PsaA metal-binding site. (a) Stereogram showing σA-weighted (2Fo–Fc) electron density (contoured at the 1.5 σ level) in the vicinity of the PsaA metal-binding site. The Zn2+ is shown in orange and the surrounding residues are in ball-and-stick representation (carbon atoms in green, oxygen in red and nitrogen in blue). Also shown (in pink) are the two water molecules hydrogen-bonded to Glu205 Oϵ1 and Asp280 Oδ2 (see text). (b) Stereogram showing the geometry of the PsaA metal-binding site. Atoms included are the four metal-coordinating residues, the DPH motifs and the water molecules associated with the metal-coordinating residues (see text). The color scheme is that of (a). The coordination geometry is highlighted by the solid black lines and potential hydrogen bonds are shown as dotted lines. The view direction is approximately that of Figure 1a. Figures were generated using MOLSCRIPT [39] and RASTER3D [40,41].
Structure 1998 6, DOI: ( /S (98) )

5. Figure 4
Stereogram showing the irregular architecture of the β strands of the C-terminal domain of PsaA. The β strands are shown in ball-and-stick representation and are labeled as stated in the text. The sidechain of Glu254 is shown, but for all other residues sidechain atoms beyond Cβ are omitted. Also included is the ordered water molecule bridging strands E and G. The color scheme is that of Figure 3. Potential hydrogen bonds (computed using the program HBPLUS [44]) are shown as dashed lines. The Figure was generated using MOLSCRIPT [39] and RASTER3D [40,41].
Structure 1998 6, DOI: ( /S (98) )