Observation of through-hydrogen-bond 2hJHC′ in a perdeuterated protein

It is demonstrated that J connectivity between amide protons and hydrogen-bond-accepting carbonyl carbons can be observed in perdeuterated human ubiquitin. A selective pulse scheme is used to detect these small (2h)J(HC') interactions in the presence of the much larger through-covalent-bond (2)J(HC') and (3)J(HC') couplings. The ratio of the observed through-H-bond correlation intensity and the (2)J(HC') connectivity observed in a reference spectrum indicates (2h)J(HC') values of ca. 0.4-0.6 Hz, which are only slightly smaller than the corresponding (3h)J(NC') values. However, for technical reasons, (2h)J(HC') couplings are more difficult to measure than (3h)J(NC'). (C) 1999 Academic Press.