免疫球蛋白IgA1在免疫系統裡扮演著重要的角色，尤以在黏膜表面對抗外來病源體的侵略為主。但部分的致病菌，如：Haemophilus influenzae及Neisseria meningitides，能夠分泌IgA1蛋白酶來切割IgA1，使失去作用，甚至造成後續免疫反應失效的嚴重後果。IgA1原蛋白酶主要由四個不同的功能區域組成：signal peptide，IgA1蛋白酶，α蛋白質及自體運輸蛋白質區域。位於C端的自體運輸蛋白質區域，又可被分為linking region（在本研究中以surface domain稱之）及β-core。過去對於IgA1蛋白酶的研究，主要集中在蛋白酶切割IgA1的作用以及C端的自體運輸功能。對於α蛋白質及surface domain並無太多的著墨。本研究即以不具IgA1蛋白酶活性的大腸桿菌（UT5600）表達重組蛋白α蛋白質及surface domain，利用人體肺部癌細胞A549進行細菌黏附作用分析，以四種不同的菌株（具有及缺少IgA1蛋白酶活性）來探討這兩個部份是否會對於細菌的黏附有所影響，進而去推測其在細菌感染上扮演的可能角色。由本研究中的結果顯示，α蛋白質及surface domain確實在對於細菌的貼附作用有著一定的作用，並且此作用會隨著菌株的不同，而具有不同的影響。

Some pathogenic bacteria including Haemophilus influenzae and Neisseria
meningitides produce a protease called IgA1 protease to impair a major antibody,
immunoglobulin A1 (IgA1), on human mucosal surfaces. The iga mRNA is
initially translated into a precursor containing four distinct domains: a 31-amino
acids signal peptide which leads the precursor to the periplasmic space, an
105-kDa protease domain which cleaves host IgA1 molecule, a β-domain
responsible for autotransportation of the protease domain, and a short linker
between the protease and the β-domains. The autotransporter β-domain can be
further divided into three subdomains in Neisseria protease: an extracellular
linking region α-protein and a membrane-embedded β-core, between which there
is a distinguished sequence called surface region. The hydrolytic function of the
protease and the transporter role of β-core had been studied extensively, but the
α-protein and the surface regions were less defined, or had their role
characterized. Thus this study is designed to reveal the possible pathogenic
functions of the α-protein and the surface region in bacterial adherence to human
cell surfaces. To complete this project, recombinant α-protein and the surface
region were expressed in IgA1 protease-negative E. coli strain (UT5600)
respectively and purified to homogeneity. These recombinant proteins were used
in cellular assays for bacterial adhesion on human lung cancer cell (A549). Four
different invasive strains of pathogenic bacteria (IgA1 protease-positive or
negative), were recruited in adherence assays to determine the effect of the
purified α-protein and the surface region on bacterial adherence to A549 cells.
Results showed that the both α-protein and the surface region played a role in
bacterial adherence in a species-dependent manner.

English abstract…………………………………………………1
Chinese abstract………………………………………………...2
Chapter 1: Introduction……..……………………………...…...3
Chapter 2: Material and methods……...……………………......6
Chapter 3: Results…………………………………...…...........13
Chapter 4: Discussion………………………………...….........40
References……………………………………………...….......43
Appendix……..………………………………………...….......46

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