June 2007

Document Type


Degree Name



Dept. of Molecular Microbiology and Immunology


Oregon Health & Science University


Both poxviruses and γ2-herpesviruses share the K3-family of viral immune evasion proteins. These proteins are characterized by an amino-terminal RING-CH domain followed by two transmembrane domains. We analyzed several human homologues of the K3-family termed membrane-associated RING-CH (MARCH) proteins. All MARCH proteins localized to subcellular membranes while several reduced surface levels of known K3-family substrates. Thus, MARCH proteins appear to be structurally and functionally homologous to viral K3 proteins. One of the major challenges in determining the function of this family is the identification of their physiological substrates. To overcome this we created a quantitative proteomics approach which can be used to identify novel substrates for both the K3- and MARCH-families. Using stable isotope labeling by amino acids in cell culture, we compared the proteome of plasma membrane, golgi, and endoplasmic reticulum membranes in the presence and absence of K5 and MARCH-VIII. Quantitative mass spectrometric protein identification from these fractions revealed that CD316 (bone marrow stromal antigen 2), CD166 (activated leukocyte cell adhesion molecule) and syntaxin-4 were consistently underrepresented in the plasma membrane of K5 expressing cells, while CD44, CD81 (TAPA-1) and B-cell receptor-associated protein 31kDa (Bap31) were consistently underrepresented in the plasma membrane of MARCH-VIII expressing cells. Furthermore, downregulation of each of these proteins was independently confirmed. Our results both identify and characterize a novel family of human ubiquitin ligase enzymes and elucidate a novel technique which can analyze this family and be easily adapted to the analysis of other cellular enzymes viral immune modulators.




School of Medicine



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