Enzyme IIB bcellobiose of the phosphoenol‐pyruvate‐dependent phosphotransferase system of Escherichia coli: Backbone assignment and secondary structure determined by three‐dimensional NMR spectroscopy

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Abstract
The assignment of backbone resonances and the secondary structure determination of the Cys 10 Ser mutant of enzyme IIBcellobiose of the Escherichia coli cellobiose‐specific phosphoenol‐pyruvate‐dependent phosphotransferase system are presented. The backbone resonances were assigned using 4 triple resonance experiments, the HNCA and HN(CO)CA experiments, correlating backbone 1H, 15N, and 13Cα resonances, and the HN(CA)CO and HNCO experiments, correlating backbone 1H,15N and 13CO resonances. Heteronuclear 1H‐NOE 1H‐15N single quantum coherence (15N‐NOESY‐HSQC) spectroscopy and heteronuclear 1H total correlation 1H‐15N single quantum coherence (15N‐TOCSY‐HSQC) spectroscopy were used to resolve ambiguities arising from overlapping 13Cα and 13CO frequencies and to check the assignments from the triple resonance experiments. This procedure, together with a 3‐dimensional 1Ha‐13Cα‐13CO experiment (COCAH), yielded the assignment for all observed backbone resonances. The secondary structure was determined using information both from the deviation of observed 1Hα and 13Cα chemical shifts from their random coil values and 1H‐NOE information from the 15N‐NOESY‐HSQC. These data show that enzyme IIBcellobiose consists of a 4‐stranded parallel β‐sheet and 5 α‐helices. In the wild‐type enzyme IIBcellobiose, the catalytic residue appears to be located at the end of a β‐strand.