Protein NMR. J(HN-HA) Coupling Constants

³J_HNHA

KARPLUS

Empirical ³J_HN-HA values and angular backbone constraints can be interconverted following well-known Karplus relationships: 93JACS7772 , 94JMRB99-104 .

³J_HN-HA=6.64*cos²(fi-60) - 1.43*cos(fi-60) + 1.86 ( 96JACS2483 ) ³J_HN-HA=6.47*cos²(fi-60) - 1.43*cos(fi-60) + 2.03 ( 97JACS6360 ) ³J_HN-HA=7.90*cos²(fi-60) - 1.05*cos(fi-60) + 0.65 ( 99JB1-14 )
where fi is the backbone torsion angle.

In addition, ⁴J_HN-HA coupling constants might provide additional yet not parametrized constraints on the psi angle ( 02JB291).

VALUES

The ³J_HN-HA coupling constants is a valuable NMR restraint to distinguish the secondary structure in proteins. The general trends are:

Alpha-helix: 4.8 Hz

3₁₀-helix: 5.6 Hz

Beta-strand: 8.5 Hz

Examples found in the bibliography: lysozyme ( 91BIO986 ) and ubiquitin ( 96JACS2483 ).

MEASUREMENT

The most simple way to measure this coupling constant in unlabeled proteins is fitting the antiphase cross-peak pattern of a phase-sensitive 2D COSY-DQF spectrum to an specific linewidth. However, because the linewidths of large proteins are largely in excess of 4-5 Hz and frequently comparable to 1H-1H coupling constants, accurate values are better measured from E.COSY cross-peaks ( 85JACS6394 ). Other widely used alternatives to be applied on labeled proteins are:

Quantitative J-correlation:

3D HNHA experiment
Cosine modulated 2D HSQC experiment ( 02JMR313-156 )
3D HA[HB,HN](CACO)NH experiment (99JACS11821) in H₂O

J-modulated experiments:

2D HMQC-J: 90JMR110-86 , 91JACS6323 , 92JB257 , 94JB871-4 , 98JB329 .

J-multiplied 2D ¹H-¹⁵N HSQC ( 99JMR243-137 ) , J-multiplied ¹H-¹⁵N 2D HMQC ( 99MRC821 and 00JMR228-146 ) and J-multiplied ¹H-¹⁵N 2D TROSY ( 01JMR60-151 ) experiments. Multiply the J_HH value by a factor N in the indirect F₁ ¹⁵N dimension.

E.COSY experiments:

3D HNCA[HA]-E.COSY experiment.
HNCA-E.COSY ( 92ANG1609 )

Simultaneous measurement of ³J_HN-HA and ³J_HN-CO from a 3D H(N)CA,CO experiment ( 98JACS3803 ). Spin-state selective.
From TOCSY or NOESY spectra ( 97JB373-10 ).
From HNCAHA experiments ( 95JB25-5 ).
From 3D DQ/ZQ + SQ-HNCA experiment ( 95JACS10389 and 02JB291 ).
2D ¹H-¹⁵N CT-HMQC experiments ( 98JB319 and 00JMR391-143 ). Related intensity-modulated HMQC and HSQC experiments has also been reported ( 00JB29 ).

RELATED TOPICS

Impact of direct refinement against ³J_HN-HA on protein structure determination ( 94JMRB99-104 )
The same dihedral angle information can be obtained from other coupling constants values:

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