Use of streptococcus pneumoniae acyl carrier protein synthase crystal structure in diagnostics, antimicrobial drug design, and biosensors

A composition, comprising a crystal of Streptococcus pneumoniae acyl carrier protein synthase having the amino acid sequence shown in SEQ ID NO:

• 1 wherein methionine is substituted with selenomethioinine,
• wherein said acyl carrier protein synthase is a homotrimer, wherein each protomer comprises the following structural motifs:
• (d) a three-stranded anti-parallel β-sheet formed by strands β1, β5, and β4;
• (e) a long α-helix that packs diagonally against said β-sheet, together with α-helices α1, α2, α3, and α4 of an anti-parallel four helical bundle;
• and
• (f) a long, extended loop with a two-strand anti-parallel β-sheet comprising strands β2 and β3,
• wherein said structural motifs (a), (b), and (c) are organized such that said long helix α4 runs through said homotrimer, and is surrounded by the remainder of said structural motifs, as shown in FIGS. 8(B) and 8(C);
• wherein when said acyl carrier protein synthase is in native form, said crystal belongs to orthorhombic space group P212121, with unit cell dimensions of a=49.8 Å, b=59.6 Å, and c=114.7 Å, or monoclinic space group C2, with unit cell dimensions of a=120.2 Å, b=62.3 Å, c=51.7 Å, and β=98.7°, and wherein said crystal has the atomic coordinates shown in Table 3 or Table 4, respectively;
• and
• wherein when said acyl carrier protein synthase is complexed with 3′,5′-adenosine diphosphate, said crystal belongs to monoclinic space group C2, with unit cell dimensions of a=120.2 Å, b=62.3 Å, c=51.7 Å, and β=98.7°, and wherein said crystal has the atomic coordinates shown in Table 5.

A method of isolating Streptococcus pneumoniae acyl carrier protein synthase, comprising:

• (a) growing said Streptococcus pneumoniae in a medium lacking methionine but containing L-selenomethionine;
• (b) preparing a cell extract of said Streptococcus pneumoniae;
• (c) centrifuging said cell extract to produce a supernatant fraction, and collecting said supernatant fraction;
• (d) chromatographing said supernatant fraction on a cation exchange column in buffer containing dithiothreitol or β-mercaptoethanol, and collecting fractions containing said Streptococcus pneumoniae acyl carrier protein synthase;
• (e) chromatographing said fractions of step (d) on a gel filtration column in buffer containing dithiothreitol or β-mercaptoethanol, and collecting fractions containing said Streptococcus pneumoniae acyl carrier protein synthase comprising L-selenomethionine.