HNcaCO_3D.nan

NAN KB; Alex Eletsky; John Glushka

Dec 19, 2024

HNcaCO_3D.nan

DOI

dx.doi.org/10.17504/protocols.io.q26g71b21gwz/v1

NAN KB¹,
Alex Eletsky²,
John Glushka²

¹Network for Advanced NMR ( NAN);
²University of Georgia

NAN-KB UGA

Network for Advanced NMR

DOI: dx.doi.org/10.17504/protocols.io.q26g71b21gwz/v1

Protocol Citation: NAN KB, Alex Eletsky, John Glushka 2024. HNcaCO_3D.nan. protocols.io https://dx.doi.org/10.17504/protocols.io.q26g71b21gwz/v1

License: This is an open access protocol distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Protocol status: Working

We use this protocol and it's working

Created: April 18, 2024

Last Modified: December 19, 2024

Protocol Integer ID: 98431

Keywords: protein nmr, assignment, backbone, amides, 15N, hsqc

Funders Acknowledgements:

NSF

Grant ID: 1946970

Disclaimer

This protocol is part of the knowledge base content of NAN: The Network for Advanced NMR ( https://usnan.nmrhub.org/ )
Specific filenames, paths, and parameter values apply to spectrometers in the NMR facility of the Complex Carbohydrate Research Center (CCRC) at the University of Georgia.

Abstract

This protocol describes running a 3D HN(CA)CO pulse sequence with sensitivity enhancement, gradient coherence selection and water flip-back with non-uniform ( NUS) sampling scheme. This produces a 3D phase-sensitive dataset that correlates backbone 1HN and 15N resonances of residue (i) with 13CO of residues (i) and (i-1). The sequential (i-1) 13CO peaks is typically weaker than intra-residue (i) 13CO peak.

Usually optional for backbone resonance assignment, but may be useful cases of poor quality HNCACB, or degenerate CA and CB shifts. Has slightly better sensitivity than HNCACB, however, 13CO shifts cannot be used to differentiate residue types. Can be acquired with NUS sampling unless sensitivity limited. 

Required isotope labeling: U-15N,13C. Samples with additional 2H labeling should use separate HNCA(CO) version with 2H decoupling.

Optimal MW is ≤  25 kDa. Larger systems may benefit from 3D TROSY-HN(CO)CA version. Compare 2D H-N planes of HNCO and TROSY-HNCO to check which one yields better S/N.

This pulse sequence can be used for:
spin system identification 
resolving signal degeneracy in 2D 15N HSQC.
backbone resonance assignment: sequential linking of spins systems based on 13CO peak matching (in conjunction with 3D HNCO. Complements linking via HNCA and HNCACB.
resonance assignment of 13CO spins
chemical shift-based secondary structure prediction (e.g. TALOS), together with other resonances

Field strength preference: though signal dispersion is usually not an issue for HN(CA)CO, higher field strength is often preferred for higher sensitivity, assuming the same probe type.

It uses the standard Bruker Topspin pulseprogram 'hncacogp3d'  

Attachments

biotop.pdf

2.5MB

NUS_poisson_gap_file...

12KB

Guidelines

The number of directly acquired points (3 TD) should be set so the acquisition time t3,max (3 AQ) is between ~50 ms (for larger proteins ~25 kDa) and ~120 ms (for smaller proteins).  Longer times may cause excessive probe and sample heating during 15N decoupling, and resolve undesirable 3JHN,HA splittings.

Since the F2(15N) is a constant-time dimension, number of acquired points 2 TD should be should be set to the largest possible value for optimal S/N. The maximum 2 TD value is 2*int(d30/in30), where d30 is the decremented delay, and in30 is the decrement value. Both d30 and in30 are computed internally accoding to pulse program code and their values are shown in ased view. Note that in30 = in10 = 1(4*SW(N)). In TopSpin 4.x the ased command would produce a warning if 2 TD is set too large, and reset the internal td2 parameter to the maximum possible value.

Since 3D HN(CA)CO only has 2 peaks per residue, NUS sampling amount can be as low as 5-10% provided there is sufficient S/N.

Individual F1(Cab)-F3(HN) or F2(N)-F3(HN) 2D planes can be acquired by setting, respectively, 2 TD or 1 TD to 1.

To check whether TROSY-HN(CA)CO or regular HN(CA)CO yields better S/N for your sample at a particular field strength, record and compare the respective 2D F2(N)-F3(HN) planes of TROSY-HNCO and regular HNCO using identical spectral parameters.

Before start

This is a simplified protocol with minimum figures. For more detailed Bruker Topspin GUI content refer to protocols: HSQC_15N.nan, HSQC_CT_13C_ali.nan, HNCO_3D.nan or HNCA_3D.nan

This protocol requires a sample is inserted, tuned/matched on 1H, 15N, and 13C channels, and shimmed. At a minimum, 1H 90° pulse width and offset O1 should be calibrated and a 1D proton spectrum with water suppression has been collected according to the protocol PRESAT_bio.nan. 

It is recommended to calibrate 1H carrier offset, 1H H2O selective flip-back pulse, as well as 1H, 13C, and 15N 90° pulse widths using the "Optimization" tab of bioTop. Alternatively, 1H 90° pulse width and offset can be calibrated using other methods, such as pulsecal or calibo1p1. Additional parameters, like 15N and 13C offsets and spectral width can be either optimized or manually entered in the "Optimization" tab of BioTop.
Note that since BioTop optimizations are saved in the dataset folder, all experiments should be created under the same dataset name when using BioTop for acquisition setup. Prior acquisition of 2D 15N HSQC, and 3D HNCO is also recommended.

Create HNcaCO experiment file

Join an existing dataset and experiment (e.g. 1D proton, 2D 15N HSQC, 2D 13C HSQC,etc) for this sample.

Open create dataset window with edc command or through menu.
Edit text in Title box.

To select starting parameter set, check 'Read parameterset' box, and click Select.  
For standard NAN parameter sets, change the Source directory at upper right corner of the window:
Source = /opt/NAN_SB/par
Click 'Select' to bring up list of parameter sets.
Select  HNcaCO_3D_NUS_xxx.par, where xxx=900,800 or 600.
Click OK at bottom of window to create the new EXPNO directory.

If not done, tune Nitrogen and Carbon channels:
Return to the 'Acquire' menu and click 'Tune' ( or type atma on command line).

Load pulse calibrations: use getprosol (step 2.1) or bioTop (steps 2.2)

Note
Loading the HNcaCO_3D_NUS_xxx.par parameter set enters the default parameters into the experiment directory. While they represent a good starting point, they may not be fully optimal or accurate for your particular sample or spectrometer hardware. The probe- and solvent-specific parameters, specifically the 1H 90° pulse length, and possibly the 13C and 15N 90° pulse lengths, along with other dependent pulse widths and powers may need to be updated. 

There are two ways of automatically updating experimental parameters:
1) Use getprosol command, which typically only updates proton pulse widths and power levels. It is most useful for running routine experiments using the default parameters.
2) Load optimized parameter from BioTop. This module allows to optimize and define additional common parameters for a given dataset that can be applied to multiple experiments.

Loading pulse widths and power levels with getprosol:

Use the calibrated proton P1 value obtained from the proton experiment ( protocol PRESAT_bio.nan) and note the standard power level attenuation in dB for P1 (PLW1);  otherwise type calibo1p1 and wait till finished.
Then execute the getprosol command:
getprosol 1H  [ calibrated P1 value]  [power level for P1]
e.g.  getprosol 1H 9.9 -13.14. 
Where for example, the calibrated P1=9.9 at power level -13.14 dB attenuation

This also loads 15N and 13C pulse widths and power levels from the 'edprosol' table, and are assumed to be sufficiently accurate.

Go togo to step #2.3 If not using BioTop 

Loading experimental parameters from BioTop:

IIf you previously performed parameter calibrations or entered parameters values manually using the "Optimizations" tab of the BioTop GUI, you can simply type btprep at the command line.

See protocol 'BioTop: calibration and acquisition parameters' and attached Bruker manual 'biotop.pdf' for details.

Inspect and adjust Parameters

Examine parameters by typing 'eda', or select the 'Acqpars'  tab and get the 'eda' view by clicking on the 'A' icon if not default.  This view shows the three dimensions, F3 (1H)  and F2 (15N) and F1 (13C) in columns.

Parameters to check:
FnTYPE - 'traditional planes' or 'non-uniform sampling' ( see step 2.5 below )
NS - minimum 2; increase for for higher signal to noise ( S/N increases as square root of NS )
DS - 32-128 'dummy' scans that are not recorded (multiple of 16); allows system to reach steady state equilibration.
SW[ppm] - 1H (F3) ~12-15 ppm; 15N (F2)  ~25-40 ppm; 13CO (F1) ~12-20 ppm; defined in bioTop
O1P - 1H H2O offset in Hz (calibrated with BioTop or calibo1p1)
O2P - 13CO offset (~173 ppm, defined in bioTop)
O3P - 15N amide offset (~115-120 ppm, defined in bioTop)
3 TD - Number of 1H time domain real points (~1024-2048, preferably 2N,  keep 3 AQ at ~50-120 ms)
2 TD - Number of 15N time domain real points (2*int(d30/in30); 2 AQ ~24ms, CT dimension)
1 TD - Number of 13CO time domain real points (1 AQ at ~20 ms or more)
DIGMOD - 'digital' ( pulse sequence does not use acqt0 correction )

Then examine the parameters in Acqpars 'ased' mode (click 'pulse' icon), or type 'ased';  
Most of the default parameters are appropriate, however it's useful to compare values in the fields against those proposed by the original parameter file and the pulseprogram. 
 
D1 - 1-2 sec
P1 - 1H 90º high power pulse (calibrated with calibo1p1 or BioTop)
SPdB1 - power level [dB] for 1H H2O flip-back shaped pulse (calibrated with BioTop)
P3 - 13C 90º high power pulse (calibrated with BioTop)
CNST21: 13CO shift ( ~173 ppm, defined in bioTop)
CNST22: 13CA shift ( ~54 ppm, defined in bioTop)
P21 - 15N 90º high power pulse (calibrated with BioTop)

Configure NUS (non-uniform sampling) - optional

After all other acquisition parameters (especially spectral widths and time-domain points) are set, change the FnTYPE parameter to 'non-uniform sampling' (type 'eda' and select 'Experimental' to get correct parameter window). 

Then select NUS in the 'eda' parameter winow and set the desired NusAMOUNT [%] sampling density. 

For adequate reconstruction, number of NUS points should be larger than the number of expected peaks. 3D HN(CA)CO yields 2 peaks per residue, thus a 100-residue protein would require more than 200 NUS points.

After this you have the option of using either the built-in sampling schedule generator in Topspin or a third-party one.

To use the built-in sampling schedule generator in TopSpin set the NUSLIST parameter to 'automatic'. The sampling schedule will then be generated at acquisition start, and will be purely random apart from point density weighting according to NusJSP and NusT2 parameters.

A better way to generate the sampling schedule is with nusPGSv8 AU program. This AU program uses NusAMOUNT and TD values of the current experiment to generate a random schedule with 'Poisson gap' point spacing, and offers additional options for point density weighting and sampling order. ( see protocol 'Poisson Gap NUS Acquisition Setup',  and attached files 'nusPGSv8' and 'poissonv3'). To use this method, type 'nusPGSv8' on the command line. You can typically accept the default values in pop-up dialog windows, since they are suitable for most applications. A schedule will be generated and will be stored to the parameter NUSLIST.

If nusPGSv8 is not installed, copy the attached file 'nusPGSv8' to your user AU directory, /opt/topspin.X.X.X/exp/stan/nmr/au/src/user, and copy the binary file 'poissonv3' to /opt/topspinX.X.X/prog/bin.

Acquire and Process Data

Type 'expt' to calculate the expected run time
Go togo to step #2.3 If necessary to re-adjust parameters  

Type 'rga' or click on 'Gain' in Topspin Acquire menu to execute automatic gain adjustment.
Type 'zg' or click on 'Run' in Topspin Acquire menu to begin acquisition.

You can always check the first FID by typing 'efp' to execute an exponential multiplied Fourier transform.  It will ask for a FID #, choose the default #1.  You can evaluate the 1D spectrum for amide proton signal to noise and water suppression. 

3D NUS data usually cannot be processed in Topspin without a separate license (see note in step 2.5). 2D planes with NUS or uniformly sampled can be processed in Topspin, though.

Also, a 2D NUS plane can be extracted from a completed 3D NUS data set with the command 'rser2d', and then processed within Topspin.

Full 3D NUS processing is usually performed using third-party processing software, such as NMRPipe together with specialized NUS reconstruction programs (SMILE, hmsIST, NESTA, etc.).

Protocol references

J.Cavanaugh, W.Fairbrother, A.Palmer, N.Skelton:  Protein NMR Spectroscopy: Principles and Practice.
Academic Press 2006 ;  Hardback ISBN: 97801216449189, eBook ISBN: 9780080471037

R.T. Clubb, V. Thanabal & G. Wagner, J. Magn. Reson. 97, 213-217 (1992)
L.E. Kay, G.Y. Xu & T. Yamazaki, J. Magn. Reson. A109, 129-133 (1994)

'nusPGSv8' written by Scott Anthony Robson 2013

Public workspaceHNcaCO_3D.nan

HNcaCO_3D.nan