The 1. 6 Å Crystal Structure of E The 1.6 Å Crystal Structure of E. coli Argininosuccinate Synthetase Suggests a Conformational Change during Catalysis  Christopher T. Lemke, P.Lynne Howell  Structure  Volume 9, Issue 12, Pages 1153-1164 (December 2001) DOI: 10.1016/S0969-2126(01)00683-9

Figure 1 The Argininosuccinate Synthetase Mechanism Step 1: The formation of activated citrulline-adenylate releases inorganic pyrophosphate. Step 2: Nucleophilic attack by the aspartate amino group forms argininosuccinate and releases AMP. Structure 2001 9, 1153-1164DOI: (10.1016/S0969-2126(01)00683-9)

Figure 2 EAS Aspartate and Citrulline Binding Sites σA-weighted |Fo| − |Fc| omit map contoured at 3σ shows the citrulline (a) and aspartate (c) binding sites. Schematic representation of the interactions between the protein and either citrulline (b) or aspartate (d). Dashed lines represent interactions between atoms, with distances given in Å. Structure 2001 9, 1153-1164DOI: (10.1016/S0969-2126(01)00683-9)

Figure 3 The EAS Monomer (a) Stereo view of the Cα trace of the EAS monomer with every 20th residue numbered. The three substrates are in stick representation. (b) Ribbon diagram of EAS monomer. (c) Topology diagram of the EAS monomer (generated by TOPS [53] with manual editing). In panels (b) and (c) the nucleotide binding and synthetase domains are colored in red and blue, respectively, the crossover from the nucleotide binding domain to the synthetase domain is in purple, and the multimerization tail is in green. In panel (b), residues corresponding to observed clinical mutations are colored in yellow. (d) Ribbon diagram of EAS monomer, with β sheets colored in orange and α helices in blue. The secondary-structure elements were defined with Swiss-PdbViewer [54] and are as follows: β1, T2–L4; β2, Q11–F17; α1, L21–Q32; β3, V36–N43; α2, D53–Y62; β4, N66–C72; α3, R73–C86; β5, N91–T93; β6, L96–Y98; α4, T101–D120; β7, N123–D127; α5, D135–T146; β8, Q151–K154; α6, T159–E164; α7, R168–C178; β9, S191–N195; β10, G198–E202; β11, E234–E241; β12, H244–N249; α8, D256–G268; β13, S275–R281; β14, A285–E292; α9, P294–G309; α10, E313–Q332; α11, S338–S353; β15, G357–R364; β16, D368–V375; α12, P397–M406; α13, R407–T424; β17, L426–S428; and β18, Q437–E439. (e) Primary-sequence alignment of E. coli and human AS. The sequences of all 35 reported species of AS were used for producing the alignment. Residues strictly conserved between the two species are represented in uppercase. Residues involved in modeled ATP, citrulline, and aspartate binding are colored red, blue, and green, respectively. The α helices and β sheets defined above are represented as blue cylinders and orange arrows, respectively. In all panels, N and C denote the N and C termini, respectively. Structure 2001 9, 1153-1164DOI: (10.1016/S0969-2126(01)00683-9)

Figure 4 Stereo Ribbon Diagram Comparison of the EAS, Asparagine Synthetase, GMP Synthetase, and NAD+ Synthetase Nucleotide Binding Domain Structures Residues 10–180 of EAS are colored in blue, residues 228–349 and 384–440 of asparagine synthetase are colored in green, residues 229–337 and 368–392 of GMP synthetase are colored in red, and residues 40–199 of NAD+ synthetase are colored in yellow. AMP is modeled in stick form. N and C denote the N and C termini, respectively. Structure 2001 9, 1153-1164DOI: (10.1016/S0969-2126(01)00683-9)

Figure 5 Comparison of Nucleotide Binding Domains Topology diagrams of lactate dehydrogenase (a), EAS (b), and NAD+ synthetase (c). Triangles and circles represent β sheets and α helices, respectively. In all panels, N and C denote the domain N and C termini, respectively. The topology of NAD+ synthetase is representative of the other N-type ATP pyrophosphatases. Structure 2001 9, 1153-1164DOI: (10.1016/S0969-2126(01)00683-9)

Figure 6 Multimerization of EAS The EAS dimer (a) and tetramer (b–d). In panels (a)–(d), each monomer is depicted in a different color. In (a) the dimer is viewed such that the red monomer is in the same orientation as the monomers of Figure 3. The tetramer is illustrated schematically along each of the mutually perpendicular 2-fold axes (b–d). In panels e and f, only the secondary-structural elements of the synthetase domain are colored. The eight four-stranded antiparallel β sheets are colored as in panels (a)–(d), the α helices of the synthetase domain are colored in light blue, and the multimerization tail is colored in gray. Structure 2001 9, 1153-1164DOI: (10.1016/S0969-2126(01)00683-9)

Figure 7 Modeling of ATP (a) Model of ATP binding to EAS. Dashed lines represent potential hydrogen bonds/salt bridges. (b) The relative positions of the three substrates bound to EAS. The distance between the ureido oxygen of citrulline and the α-phosphate of ATP is shown as a dotted line. Structure 2001 9, 1153-1164DOI: (10.1016/S0969-2126(01)00683-9)