Upon penetration of the human body with infectious pathogens a distinct upregulation of Interferon gamma, an inflammatory cytokine, leads to a high level expression of the human guanylate binding protein 1 (hGBP1) in the target cell. Cell biological data yield vague information about the hGBP1's integration into host defense, but the diversity in defensive effects (e.g. antiviral and -bacterial, tumor growth inhibitive) is pointing to a great importance in innate immunity. The biochemistry of hGBP1 in vitro is well characterized. Beside GTP binding and hydrolysis a characteristic property of hGBP1 is its ability to selfassemble. In the course of GTP hydrolysis oligomerisation occurs in a highly concentration depedent manner accelerating of hydrolysis. Morerover, it was found that this process involves extensive conformational changes inside the protein.To study these intra- and intermolecular conformational changes - meaning changes in the distance - via fluorescence resonance energy transfer multiparameter fluorescence detection under single molecule conditions as well as other advanced fluorescent techniques were applied. Therefore cysteines were introduced at distinct positions by site-directed mutagenesis and labelled with a FRET dye pair and measurements were performed in the presence of different nucleotide analogues. Also, the dependence on the protein concentration was subjected.It could be shown that the protein quickly oscillates around the conformation seen in x-ray data. In the presence of GppNHp or GDP AlFx the molecules appeared to be fixed in the open conformation. Various intramolecular and intermolecular distances could be extracted. In the presence of GppNHp either dependence on nucleotide concentration and protein concentration was found. These data allow conclusions about the overall oligomerisation dependent structural and dynamic changes inside hGBP1.