scholarly journals Structure and Ligand-Binding Properties of the O Antigen ABC Transporter Carbohydrate-Binding Domain

Structure ◽  
2020 ◽  
Vol 28 (2) ◽  
pp. 252-258.e2 ◽  
Author(s):  
Yunchen Bi ◽  
Jochen Zimmer
2020 ◽  
Vol 118 (1) ◽  
pp. e2016144118
Author(s):  
Christopher A. Caffalette ◽  
Jochen Zimmer

O antigens are important cell surface polysaccharides in gram-negative bacteria where they extend core lipopolysaccharides in the extracellular leaflet of the outer membrane. O antigen structures are serotype specific and form extended cell surface barriers endowing many pathogens with survival benefits. In the ABC transporter-dependent biosynthesis pathway, O antigens are assembled on the cytosolic side of the inner membrane on a lipid anchor and reoriented to the periplasmic leaflet by the channel-forming WzmWzt ABC transporter for ligation to the core lipopolysaccharides. In many cases, this process depends on the chemical modification of the O antigen’s nonreducing terminus, sensed by WzmWzt via a carbohydrate-binding domain (CBD) that extends its nucleotide-binding domain (NBD). Here, we provide the cryo-electron microscopy structure of the full-length WzmWzt transporter fromAquifex aeolicusbound to adenosine triphosphate (ATP) and in a lipid environment, revealing a highly asymmetric transporter organization. The CBDs dimerize and associate with only one NBD. Conserved loops at the CBD dimer interface straddle a conserved peripheral NBD helix. The CBD dimer is oriented perpendicularly to the NBDs and its putative ligand-binding sites face the transporter to likely modulate ATPase activity upon O antigen binding. Further, our structure reveals a closed WzmWzt conformation in which an aromatic belt near the periplasmic channel exit seals the transporter in a resting, ATP-bound state. The sealed transmembrane channel is asymmetric, with one open and one closed cytosolic and periplasmic portal. The structure provides important insights into O antigen recruitment to and translocation by WzmWzt and related ABC transporters.


2007 ◽  
Vol 406 (2) ◽  
pp. 209-214 ◽  
Author(s):  
Lavinia Cicortas Gunnarsson ◽  
Cedric Montanier ◽  
Richard B. Tunnicliffe ◽  
Mike P. Williamson ◽  
Harry J. Gilbert ◽  
...  

Molecular engineering of ligand-binding proteins is commonly used for identification of variants that display novel specificities. Using this approach to introduce novel specificities into CBMs (carbohydrate-binding modules) has not been extensively explored. Here, we report the engineering of a CBM, CBM4-2 from the Rhodothermus marinus xylanase Xyn10A, and the identification of the X-2 variant. As compared with the wild-type protein, this engineered module displays higher specificity for the polysaccharide xylan, and a lower preference for binding xylo-oligomers rather than binding the natural decorated polysaccharide. The mode of binding of X-2 differs from other xylan-specific CBMs in that it only has one aromatic residue in the binding site that can make hydrophobic interactions with the sugar rings of the ligand. The evolution of CBM4-2 has thus generated a xylan-binding module with different binding properties to those displayed by CBMs available in Nature.


2019 ◽  
Vol 294 (41) ◽  
pp. 14978-14990 ◽  
Author(s):  
Evan Mann ◽  
Steven D. Kelly ◽  
M. Sameer Al-Abdul-Wahid ◽  
Bradley R. Clarke ◽  
Olga G. Ovchinnikova ◽  
...  

PLoS ONE ◽  
2010 ◽  
Vol 5 (4) ◽  
pp. e10361 ◽  
Author(s):  
Justina C. Wolters ◽  
Ronnie P-A. Berntsson ◽  
Nadia Gul ◽  
Akira Karasawa ◽  
Andy-Mark W. H. Thunnissen ◽  
...  

2003 ◽  
Vol 284 (5) ◽  
pp. L871-L881 ◽  
Author(s):  
Rebecca E. Oberley ◽  
Jeanne M. Snyder

Surfactant protein (SP)-A is a member of the collectin family of proteins and plays a role in innate host defense of the lung. SP-A binds to the carbohydrates of lung pathogens via its calcium-dependant carbohydrate-binding domain. Native human alveolar SP-A consists of two distinct gene products: SP-A1 and SP-A2; however, only SP-A2 is expressed in the submucosal glands of the conducting airways. The function of the isolated SP-A2 protein is unknown. We hypothesized that SP-A1 and SP-A2 might have different carbohydrate-binding properties. In this study, we characterized the carbohydrate-binding specificities of native human alveolar SP-A and recombinant human SP-A1 and SP-A2 in the presence of either 1 or 5 mM Ca2+. We found that all of the SP-A proteins bind carbohydrates but with different affinities. All of the SP-A proteins bind to fucose with the greatest affinity. SP-A2 binds with a higher affinity to a wider variety of sugars than SP-A1 at either 1 or 5 mM Ca2+. These findings are suggestive that SP-A2 may interact with a greater variety of pathogens than native SP-A.


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