The Marine Science Institute, College of Science, University of the Philippines Diliman, Quezon City, Philippines.
Med Hypotheses. 2010 Feb;74(2):240-1. doi: 10.1016/j.mehy.2009.09.034. Epub 2009 Oct 9.
The relative mildness of the pandemic 2009 (H1N1) swine influenza virus compared to the 1918 pandemic (H1N1) virus may be due to a variety of possible causes, including the existence of effective immunity in the host, the lessened ability of the virus to bind to target cells or to replicate in them, a diminished secretion of molecules that could cause further complications like pneumonia, etc. A comparison of the hemagglutinin sequences from the pandemic 2009 (H1N1) viruses with that of the 1918 (H1N1) virus reveals a difference in the residues occupying position 200, which has been shown to be involved in receptor binding. In all the pandemic 2009 (H1N1) hemagglutinin sequences available in the NCBI database, position 200 is occupied by serine. In the hemagglutinin of the 1918 (H1N1) virus, position 200 is occupied by proline. A proline-to-serine substitution could introduce a significant structural change in the receptor-binding site of the hemagglutinin, which could reduce the receptor-binding ability of the 2009 (H1N1) virus. It is proposed that this substitution is the cause of the relative avirulence of the 2009 (H1N1) virus compared to the 1918 (H1N1) virus.
2009 年（H1N1）猪流感病毒相对温和，与 1918 年大流行（H1N1）病毒相比，可能有多种原因，包括宿主存在有效免疫、病毒与靶细胞结合或在其中复制的能力减弱、可能导致肺炎等进一步并发症的分子分泌减少等。比较大流行 2009 年（H1N1）病毒与 1918 年（H1N1）病毒血凝素序列发现，在 200 位残基处存在差异，该残基被证明参与受体结合。在 NCBI 数据库中所有可用的大流行 2009 年（H1N1）血凝素序列中，200 位由丝氨酸占据。1918 年（H1N1）病毒的血凝素中，200 位由脯氨酸占据。脯氨酸到丝氨酸的取代可能会导致血凝素受体结合位点发生重大结构变化，从而降低 2009 年（H1N1）病毒的受体结合能力。有人提出，这种取代是导致 2009 年（H1N1）病毒相对弱毒与 1918 年（H1N1）病毒的原因。
