Journal of Life Science (생명과학회지)

Korean Society of Life Science (한국생명과학회)
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C-terminal Fusion of EGFP to Pneumolysin from Streptococcus pneumoniae modified its Hemolytic Activity

Streptococcus pneumoniae가 생산하는 pneumolysin의 EGFP 융합으로 인한 용혈활성 변화

  • Chung, Kyung Tae (Department of Clinical Laboratory Science, Dong-Eui University) ;
  • Lee, Jae Heon (Department of Diagnosis, Dongguk University Gyeongju Hospital) ;
  • Jo, Hye Ju (Department of Diagnostic Laboratory Medicine, Dong-A University Hospital)
  • Received : 2017.08.08
  • Accepted : 2017.11.17
  • Published : 2018.01.30
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Abstract

Streptococcus pneumoniae is one of the major pathogens in community-acquired diseases, and it contains several factors that promote its pathogenesis, including pneumolysin (PLY). PLY is a member of the cholesterol-dependent cytolysin family, which attacks cholesterol-containing membranes, thereby forming ring-shaped pores. Thus, it is a major key target for vaccines against pneumococcal disease. We cloned the PLY gene from S. pneumoniae D39 and inserted it into the pQE-30 vector. Recombinant PLY (rPLY) was overexpressed in Escherichia coli M15 and purified by $Ni^{2+}$ affinity chromatography. Similarly, a PLY-EGFP fusion gene was produced by inserting the EGFP gene at the 3' end of the PLY gene in the same vector, and the recombinant protein was purified. Sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE) showed that both recombinant proteins were purified. rPLY exhibited significant hemolytic activity against 1% human red blood cells (RBCs). Complete hemolysis was obtained at 500 ng/ml, and 50% hemolysis was found with a 240 ng/ml concentration. In contrast, rPLY-EGFP did not show hemolytic activity. However, rPLY-EGFP did bind the RBC membrane, indicating that rPLY-EGFP lost hemolytic activity via EGFP fusion, while retaining its membrane-binding ability. These data suggest that PLY's C terminus is important for its hemolytic activity. Therefore, these two recombinant proteins can be extremely useful for investigating the toxin mechanism of PLY and cell damage during pneumonia.

Streptococcus pneumoniae는 pneumolysin과 같은 병원성 인자를 가지고 있으며, 지역사회에서 전파되는 심각한 병원성균에 포함된다. Pneumolysin (PLY)은 콜레스테롤 의존적으로 세포막에 구멍을 형성하는 세포독소로서 백신의 주요한 표적 항원이다. PLY의 연구를 위하여 Streptococcus pneumoniae D39 균주에서 추출한 genomic DNA를 주형으로 하여 PCR을 시행하였다. 합성된 PLY 유전자 DNA를 pQE-30 vector에 삽입하고, E. coli M15에 형질전환 시킨 후 LB 배지에 IPTG를 첨가하여 PLY 단백질을 생산하였다. 재조합 단백질은 $Ni^{2+}$-agarose column을 사용하여 정제하였다. 또한, EGFP를 PLY C-말단에 부착한 융합단백질도 동일한 방법으로 클로닝하여 재조합 단백질을 생산하였다. 500 ng/ml 농도의 재조합 PLY는 1.0% 적혈구 현탁액을 100% 용혈시켰으며, 240 ng/ml 농도는 50% 용혈을 나타내었다. 그러나 재조합 PLY-EGFP는 용혈 활성이 전혀 나타나지 않았으나 형광현미경으로 관찰하였을 때 적혈구 막에 결합되어 있었다. 즉, EGFP의 PLY C-말단 부착은 PLY의 세포막 결합능은 유지시켰으나 용혈기능은 방해하였다. PLY C-말단은 용혈기능에 아주 중요한 영역이며, 세포막 결합은 PLY의 다른 영역이 보다 중요하게 작용할 것으로 추측된다. 따라서, 육안으로 관찰이 가능한 결합능은 가졌으나 용혈 기능이 결여된 PLY-EGFP를 대조군으로 활용함으로써 두 재조합 단백질은 폐렴 유발에 있어서 PLY 작용 연구에 사용될 수 있을 것으로 기대된다.

Keywords

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