人類多瘤性病毒JC病毒主要殼体蛋白VP1基因己被選殖到酵母菌細胞表達，且VP1蛋白質在酵母菌細胞內可自我組裝為類似殼体構造(capsid-like particle)，可與人類O型紅血球細胞產生凝集。以CsCl密度梯度離心分析顯示此殼体構造含有類似完整病毒顆粒(virion-like pseudovirion)，密度1.34 g/cm3及空殼病毒顆粒(empty capsid-like pseudocapsid)，密度1.29 g/cm3的兩群蛋白質。以10-30%蔗糖梯度離心可純化這兩群蛋白質。電子顯微鏡觀察外形則見pseudovirion及pseudocapsid兩種構造。核酸萃取分析顯示pseudovirion包含有DNA及RNA。pseudocapsid可攜帶外生性DNA到人類胎兒腎臟細胞。此外，VP1蛋白質以2D-PAGE分析共有6個species。為了探討雙硫鍵在JCV殼体內的存在性及角色，以EGTA及DTT同時處理VP1殼体，會使其瓦解為capsomere。加入鈣離子會使capsomere部份重組成capsid。若加入EGTA於再重組的capsid，不需DTT即可使capsid再瓦解為capsomere。先以DTT處理capsid，再加入EGTA，會使capsid完全瓦解為capsomere；先EGTA再DTT處理則不會導致capsid瓦解。因此推測雙硫鍵可保護鈣離子被EGTA螯合，而鈣離子為形成殼體結構所必需。以non-reducing SDS-PAGE分析VP1殼体，發現VP1 monomer、dimer及trimer皆存在於殼體內且各占VP1分子的45、40及15%，顯示一半的VP1蛋白質形成雙硫鍵鍵結。non-reducing SDS-PAGE分析DTT處理的殼体，全部都是VP1 monomer，以電顯圖觀察DTT處理的殼体，發現仍保有完整殼體結構但其殼体膨脹約4.5%，可能因而喪失保護鈣離子被螯合的功能。non-reducing gel分析capsomere，只有VP1 monomer存在，顯示，capsomere內並沒有雙硫鍵。diamine處理capsomere，會使capsomere的雙硫鍵再形成。顯示，capsid內的雙硫鍵鍵結是存在於capsomere與capsomere之間。
由這些結果推測，VP1蛋白質的dimerization及trimerization係由capsomere之間(Intercapsomeric)的雙硫鍵鍵結而形成。雙硫鍵可穩定殼体構造且保護二價鈣離子，而鈣離子在capsid組裝扮演決定性角色。
The major capsid protein VP1 of human polyomavirus, JC virus, has been cloned and expressed in yeast cells. VP1 protein expressed in yeast was able to self-assemble into a capsid-like structure and cause hemagglutination.The capsid-like particles were comprised of virion-like and empty capsid-like particles with 1.34 and 1.29 g/cm3 of density respectively. Morphology of the particles has been observed by electron microscopy.The virion-like particles contained host DNA and RNA molecules.The empty capsid-like particles were able to package and deliver exogeneous DNA into human kidney 293 cell. JCV capsid could be disrupted into pentameric capsomeres in the presence of both EGTA and DTT but the roles of metal ion and disulfide in capsid are still not known. In this study, disulfide linkage was found in the VP1 capsid as demonstrated by non-reducing gel. Capsid treated with DTT remained structural integrity but the disulfide has been abolished. Subsequently, the DTT treated capsid could be dissociated into capsomeres by EGTA alone. In addition, capsomeres were able to re-assemble into capsid-like particle in the presence of calicium ions. The re-assembled capsid without disulfide could be disrupted into capsomeres by EGTA alone. These results indicate that calcium ion is essential for capsid formation and disulfide is crucial for keeping capsid integrity and presumably protects calcium ion from chelation.
