Matching Peaks

You can use the Match Peaks function in order to find possible neighbouring residues to your starting residue. Simply select the diagonal peak of your starting residue in the 15N-NOESY-HSQC and the NOE you are interested in. Then right-click the mouse over one of the peaks and go to Locate Peaks, Match multiple peaks, In 15N_NOESY, F2 (in older versions of analysis right-click and go to Peaks, Match Peaks, …). Note that the 15N_NOESY part is the Experiment Name you gave your 15N-NOESY-HSQC and that the search dimension should be the indirect 1H dimension – this will usually be F2, but this may not always be the case – it depends on exactly how you recorded your experiment.

Searching for matches in the 15N-NOESY-HSQC spectrum

Analysis will now look through the F2 dimension of your 15N-NOESY-HSQC peak list and look for matches to your query peaks. The results are brought up in the Group Peaks pop-up. You will see a list of peaks sorted by a score – the higher the score, the better the match. And of course you are interested in both peaks matching, so results in which two peaks can be matched are better than ones where only one matches. You can now select a group of peaks that you would like to inspect visually. You can have them automatically brought up as strips in a window of your choice. Make sure the Target Window is the one you would like to use and then click on Display Groups in Strips.

The Match Peaks results pop-up

When investigating the strips (below) it is easily visible that only spin system {25} can be the correct match.

Strips of the matched peaks results

Make a note of the matching spin system, check for information on the directionality ({19} has a strong NOE to the Hα of {25}, so {19} is probably C-terminal to {25}) and then check for matches to the other NOEs in the {19} strip.

It is probably also worth assigning the NOESY peaks that link the two spin systems for future reference. Bring up the Assignment Panel (hold the mouse over the peak in question and then press a) and select the relevant resonance in the F2 dimension.

Assigning a NOESY peak in the 15N-NOESY-HSQC

You can also set a sequential link between the two spin systems if you are confident that they are neighbours and that you know the directionality. Simply hold the mouse over the NOESY peak linking the two spin systems and right-click the mouse and go to Assign, Set sequential spin systems and select the option from the list which correctly describes which dimension belongs to residue i +/- 1 relative to the other two dimensions. Probably you will need to select either F1 0, F2 -1, F3 0 or F1 0, F2 +1, F3 0.

Setting a sequential link in the 15N-NOESY-HSQC