McMurry L M, Stephan M, Levy S B
Department of Molecular Biology, Tufts University School of Medicine, Boston, Massachusetts 02111.
J Bacteriol. 1992 Oct;174(19):6294-7. doi: 10.1128/jb.174.19.6294-6297.1992.
The aspartate 15 residue within the first predicted intramembrane helix of the tetracycline efflux protein Tet has been conserved in four tetracycline resistance determinants from gram-negative bacteria. Its replacement in class B Tet by tyrosine, histidine, or asparagine resulted in a 60 to 85% loss of tetracycline resistance and a similar loss of tetracycline-proton antiport. The tyrosine and histidine substitutions lowered the Vmax of the efflux system by some 90% but did not alter the Km. The asparagine substitution raised the Km over 13-fold, while the Vmax was equal to or greater than that of the wild type. Therefore, although the nature of its role is unclear, aspartate 15 is important for normal Tet function.
四环素外排蛋白Tet第一个预测的跨膜螺旋内的天冬氨酸15残基，在革兰氏阴性菌的四个四环素抗性决定簇中是保守的。在B类Tet中，用酪氨酸、组氨酸或天冬酰胺取代该残基，导致四环素抗性丧失60%至85%，四环素-质子反向转运也有类似程度的丧失。酪氨酸和组氨酸取代使外排系统的Vmax降低约90%，但不改变Km。天冬酰胺取代使Km升高超过13倍，而Vmax等于或大于野生型。因此，尽管其作用性质尚不清楚，但天冬氨酸15对Tet的正常功能很重要。
