The investigation of the physiological function of GBP28 which is specific for adipose tissue

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Human GBP28, a novel plasma gelatini-binding protein, exists in a homo-trimer through its collagen-like domain and further combines to make oligomeric complexes. In order to examine the molecular basis for the complex formation, human GBP28 has been overexpressed in Chinese hamster ovary cells. The recombinant wild-type GBP28 is post-translationally processed in the same way as the native protein. Although the glycosylation of recombinant wild-type GBP28 is slightly different from native GBP28, the oligomerization of trimeric recombinant wild-type GBP28 was observed. The substitution Cys^<152> to Ser indicated that the mutated protein could not form the trimeric structural unit, and did not assemble into higher order structures. Although the mutated GBP28 DNA was transcribed as well as wild-type GBP28 DNA, the substitution decreased the amount of detectable recombinant GBP28, whose mechanism was unknown. In the case of Cys36Ser-mutated GBP28, the recombinant protein was not detected by Western-blot at all. These results strongly indicate that the Cys36 residue is essential for the polypeptide folding of GBP28 molecule..