AN INTRODUCTION

1. Submitted by
Fazilat Javed
Roll #
3003
Submitted to
Sir Inam-ul -haq
UNIVERSITY OF EDUCATION OKARA CAMPUS 1

2. Contents
 Introduction
 Importance of NMR chemical shift re-referencing in
biomolecular NMR
 Programs for protein chemical shift re-referencing
 SHIFTCOR: A structure-based chemical shift
correction program
 SHIFTCOR output
 Structure-independent chemical shift correction
programs
 References
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3. Introduction
 Protein chemical shift re-referencing is a post-
assignment process of adjusting the assigned NMR
chemical shifts to match IUPAC and BMRB
recommended standards in protein chemical shift
referencing. In NMR chemical shifts are normally
referenced to an internal standard that is dissolved in
the NMR sample.
 Chemical shift re-referencing offers a means to correct
these referencing errors and to standardize the
reporting of protein chemical shifts across
laboratories.
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4. Importance of NMR chemical shift
re-referencing
 Incorrect chemical shift referencing is a particularly acute
problem in biomolecular NMR. It has been estimated that
up to 20% of 13C and up to 35% of 15N shift assignments are
improperly referenced. Given that the structural and
dynamic information contained within chemical shifts is
often quite subtle.
 It is critical that protein chemical shifts be properly
referenced so that these subtle differences can be detected.
Fundamentally, the problem with chemical shift
referencing comes from the fact that chemical shifts are
relative frequency measurements rather than absolute
frequency measurements.
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5. Programs for protein chemical
shift re-referencing
 Because of the magnitude and severity of the problems
with chemical shift referencing in biomolecular NMR,
a number of computer programs have been developed
to help mitigate the problem.
 The first program to comprehensively tackle chemical
shift mis-referencing in biomolecular NMR was
shiftor.
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6. SHIFTCOR: A structure-based
chemical shift correction program
 SHIFTCOR is an automated protein chemical shift
correction program that uses statistical methods to
compare and correct predicted NMR chemical shifts
(derived from the 3D structure of the protein) relative
to an input set of experimentally measured chemical
shifts.
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7. UNIVERSITY OF EDUCATION OKARA CAMPUS 7
NMR Monitors the Different Physical Properties That Exist
Between a Protein and a Ligand
NMR Analysis of Protein-Ligand Interactions

8. Procedure of shift prediction
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9. SHIFTCOR output
 SHIFTCOR generates and reports chemical shift offsets or
differences for each nucleus. The results contain the
chemical shift analyses and the corrected BMRB formatted
chemical shift file.
 SHIFTCOR uses the chemical shift calculation program
SHIFTX to predict 1Hα, 13Cα,15N shifts based on the 3D
structure coordinates of the protein being analyzed.
 By comparing the predicted shifts to the observed shifts,
SHIFTCOR is able to accurately identify chemical shift
reference offsets as well as potential mis-assignments.
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10. Structure-independent chemical
shift correction programs
The PSSI and PANAV programs use the secondary
structure determined by 1H shifts to adjust the target
protein’s 13C and 15N shifts to match the 1H-derived
secondary structure. LACS uses the difference between
secondary 13Cα and 13Cβ shifts plotted against
secondary 13Cα shifts or secondary 13Cβ shifts to
determine reference offsets. A more recent version of
LACS [68] has been adapted to identify 15N chemical
shift mis-referencing. This new version of LACS
exploits the well-known relationship between 15N
shifts and the 13Cα (or 13Cβ shifts of the preceding
residue.
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11. Conclusions
 The method of re-referencing we introduce a
statistical procedure that relies on average behaviour
of sample population and is used to identify to a
statistically significant degree.
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12. References
 "CheckShift: automatic correction of inconsistent
chemical shift referencing.". Journal of Biomolecular
NMR. (31-1-2015)
 Moseley, NH; Sahota G; Montelione TG (31-1-2015).
 www.wikipedia.com
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