3Q8A

Crystal structure of WT Protective Antigen (pH 5.5)

Summary for 3Q8A

• Entry DOI: 10.2210/pdb3q8a/pdb
• Related: 3q8b 3q8c 3q8e 3q8f
• Descriptor: Protective antigen, CALCIUM ION (2 entities in total)
• Functional Keywords: protective antigen, anthrax, ph stability, protein binding, toxin
• Biological source: Bacillus anthracis (anthrax,anthrax bacterium)
• Cellular location: Secreted, extracellular space: P13423
• Total number of polymer chains: 1
• Total formula weight: 82848.98

Authors

Rajapaksha, M.,Lovell, S.,Janowiak, B.E.,Andra, K.K.,Battaile, K.P.,Bann, J.G. (deposition date: 2011-01-06, release date: 2012-01-18, Last modification date: 2023-09-13)

Primary citation

Rajapaksha, M.,Lovell, S.,Janowiak, B.E.,Andra, K.K.,Battaile, K.P.,Bann, J.G.
pH effects on binding between the anthrax protective antigen and the host cellular receptor CMG2.
Protein Sci., 21:1467-1480, 2012

PubMed Abstract: The anthrax protective antigen (PA) binds to the host cellular receptor capillary morphogenesis protein 2 (CMG2) with high affinity. To gain a better understanding of how pH may affect binding to the receptor, we have investigated the kinetics of binding as a function of pH to the full-length monomeric PA and to two variants: a 2-fluorohistidine-labeled PA (2-FHisPA), which is ∼1 pH unit more stable to variations in pH than WT, and an ∼1 pH unit less stable variant in which Trp346 in the domain 2β(3) -2β(4) loop is substituted with a Phe (W346F). We show using stopped-flow fluorescence that the binding rate increases as the pH is lowered for all proteins, with little influence on the rate of dissociation. In addition, we have crystallized PA and the two variants and examine the influence of pH on structure. In contrast to previous X-ray studies, the domain 2β(3) -2β(4) loop undergoes little change in structure from pH ∼8 to 5.5 for the WT protein, but for the 2-FHis labeled and W346F mutant there are changes in structure consistent with previous X-ray studies. In accord with pH stability studies, we find that the average B-factor values increase by ∼20-30% for all three proteins at low pH. Our results suggest that for the full-length PA, low pH increases the binding affinity, likely through a change in structure that favors a more "bound-like" conformation.

PubMed: 22855243
DOI: 10.1002/pro.2136

Experimental method

X-RAY DIFFRACTION (3.129 Å)