1xuu: Difference between revisions

[[Image:1xuu.jpg|left|200px]]<br /><applet load="1xuu" size="350" color="white" frame="true" align="right" spinBox="true"  

In Neisseria meningitidis and related bacterial pathogens, sialic acids play critical roles in mammalian cell immunity evasion and are synthesized by a conserved enzymatic pathway that includes sialic acid synthase (NeuB, SiaC, or SynC). NeuB catalyzes the condensation of phosphoenolpyruvate (PEP) and N-acetylmannosamine, directly forming N-acetylneuraminic acid (or sialic acid). In this paper we report the development of a coupled assay to monitor NeuB reaction kinetics and an 18O-labeling study that demonstrates the synthase operates via a C-O bond cleavage mechanism. We also report the first structure of a sialic acid synthase, that of NeuB, revealing a unique domain-swapped homodimer architecture consisting of a (beta/alpha)8 barrel (TIM barrel)-type fold at the N-terminal end and a domain with high sequence identity and structural similarity to the ice binding type III antifreeze proteins at the C-terminal end of the enzyme. We have determined the structures of NeuB in the malate-bound form and with bound PEP and the substrate analog N-acetylmannosaminitol to 1.9 and 2.2 A resolution, respectively. Typical of other TIM barrel proteins, the active site of NeuB is located in a cavity at the C-terminal end of the barrel; however, the positioning of the swapped antifreeze-like domain from the adjacent monomer provides key residues for hydrogen bonding with substrates in the active site of NeuB, a structural feature that leads to distinct modes of substrate binding from other PEP-utilizing enzymes that lack an analogous antifreeze-like domain. Our observation of a direct interaction between a highly ordered manganese and the N-acetylmannosaminitol in the NeuB active site also suggests an essential role for the ion as an electrophilic catalyst that activates the N-acetylmannosamine carbonyl to the addition of PEP.

1XUU is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Neisseria_meningitidis Neisseria meningitidis] with <scene name='pdbligand=MN:'>MN</scene> and <scene name='pdbligand=MLT:'>MLT</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1XUU OCA].  

[[Category: Lovering, A L.]]

[[Category: Strynadka, N C.]]

[[Category: Tanner, M E.]]

[[Category: Wakarchuk, W W.]]

''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 15:58:52 2008''