Introduction:
Determining the structure of a protein at atomic resolution is crucial for understanding its function and designing drugs. Several techniques are available for this purpose, including Raman spectroscopy, IR spectroscopy, UV spectroscopy, and NMR spectroscopy. Among these, NMR spectroscopy is the most suitable for determining the structure of a 15 kDa globular protein at atomic resolution.

NMR Spectroscopy:
1. Principle: Nuclear Magnetic Resonance (NMR) spectroscopy is based on the interaction of atomic nuclei with an external magnetic field. When placed in a strong magnetic field, atomic nuclei absorb and emit electromagnetic radiation at specific frequencies, depending on their chemical environment.

2. Protein Structure Determination:
NMR spectroscopy can be used to determine the structure of a protein by measuring the interactions between different atomic nuclei within the protein. In the case of a 15 kDa globular protein, the technique used is called solution-state NMR spectroscopy.

3. Isotopic Labeling:
To obtain high-resolution NMR spectra, isotopic labeling is typically used. This involves incorporating stable isotopes, such as 15N and 13C, into the protein during expression. Isotopic labeling increases the number of NMR signals and simplifies the interpretation of spectra.

4. Resonance Assignment:
The first step in protein structure determination by NMR is resonance assignment. This involves identifying and assigning the NMR signals to specific atoms in the protein. By analyzing the chemical shifts and coupling patterns of the NMR signals, the amino acid sequence of the protein can be determined.

5. Distance Restraints:
Once the resonance assignment is complete, distance restraints between pairs of atoms can be derived from the NMR data. These restraints provide information about the spatial arrangement of atoms within the protein.

6. Structure Calculation:
Using the distance restraints and other experimental data, computational methods can be employed to calculate a set of structures that satisfy the restraints. This process is known as structure calculation.

7. Structure Refinement:
The calculated structures are then refined using molecular dynamics simulations and energy minimization techniques. This step further improves the accuracy and reliability of the final protein structure.

Conclusion:
In summary, NMR spectroscopy is the most suitable technique for determining the structure of a 15 kDa globular protein at atomic resolution. It allows for the determination of the protein's three-dimensional structure by measuring the interactions between atomic nuclei. Isotopic labeling, resonance assignment, distance restraints, structure calculation, and structure refinement are the key steps involved in this process. NMR spectroscopy provides valuable insights into the structure-function relationship of proteins and is widely used in structural biology and drug discovery.