蛋白質A

現有可用的蛋白結構：
PDB	1dee, 1l6x

Protein A
Protein A
	Structure of a domain of protein A as a three-helix bundle binding to the heavy variable chain of a VH3 human Fab left. Minimized protein A bound to Fc fragment of Rituximab.
鑑定
標誌	SpA
SCOP（英語：Structural Classification of Proteins）	1DEE / SUPFAM
PDB
現有可用的蛋白結構：
PDB	1dee, 1l6x

蛋白質A（英語：Protein A）為金黃色葡萄球菌表面上發現的一種表面蛋白，大小約為42 kDa。該蛋白由 spa 基因轉譯而成，並由DNA的拓樸結構、包內滲透壓，以及一個名為ArlS-ArlR的雙單元調控系統（英語：two-component regulatory system）調控。該蛋白可以與免疫球蛋白結合，故常用於生化研究。該蛋白三維構造中有五個同源性免疫球蛋白結合域，每個結合域都能與多種哺乳類的免疫球蛋白結合，最主要為IgG。蛋白質A能與大多數免疫球蛋白重鏈的Fc區域（英語：Fc region）結合，甚至可與人類VH3蛋白質家族的Fab區域（英語：Fab region）結合。當蛋白質A與免疫球蛋白結合後，這些免疫球蛋白便失去了作用，進而摧毀免疫系統的吞噬作用及調理作用（英語：opsonization）。

參考文獻

^ Graille M, Stura EA, Corper AL, Sutton BJ, Taussig MJ, Charbonnier JB, Silverman GJ. Crystal structure of a Staphylococcus aureus protein A domain complexed with the Fab fragment of a human IgM antibody: structural basis for recognition of B-cell receptors and superantigen activity. Proceedings of the National Academy of Sciences of the United States of America. May 2000, 97 (10): 5399–404. PMC 25840  . PMID 10805799. doi:10.1073/pnas.97.10.5399.
^ Idusogie EE, Presta LG, Gazzano-Santoro H, Totpal K, Wong PY, Ultsch M, Meng YG, Mulkerrin MG. Mapping of the C1q binding site on rituxan, a chimeric antibody with a human IgG1 Fc. Journal of Immunology. April 2000, 164 (8): 4178–84. PMID 10754313. doi:10.4049/jimmunol.164.8.4178.

[pmid10805799-1] Graille M, Stura EA, Corper AL, Sutton BJ, Taussig MJ, Charbonnier JB, Silverman GJ. Crystal structure of a Staphylococcus aureus protein A domain complexed with the Fab fragment of a human IgM antibody: structural basis for recognition of B-cell receptors and superantigen activity. Proceedings of the National Academy of Sciences of the United States of America. May 2000, 97 (10): 5399–404. PMC 25840  . PMID 10805799. doi:10.1073/pnas.97.10.5399.

[pmid10754313-2] Idusogie EE, Presta LG, Gazzano-Santoro H, Totpal K, Wong PY, Ultsch M, Meng YG, Mulkerrin MG. Mapping of the C1q binding site on rituxan, a chimeric antibody with a human IgG1 Fc. Journal of Immunology. April 2000, 164 (8): 4178–84. PMID 10754313. doi:10.4049/jimmunol.164.8.4178.

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