Protein Structure in THz-TDS

Calmodulin, or calcium modulated protein (CaM), is a hinge protein that takes on several different structures, which makes it a good choice to measure THz TDS measurements of internal structural vibrations.  The main role of the protein is to regulate biological processes like metabolism and nerve growth.  The protein itself has 3 distinct shapes.  The first structure is the natural structure that has no bonding with other substances (See Figure 1).  The second occurs when four calcium atoms bond to the calmodulin (See Figure 2).  This causes the original structure to bend to a dumbbell shape.  From here, the third shape is achieved by a bond with a substrate, or polypeptide.  A polypeptide is a chain of amino acids bound with peptide bonds.  They can bind together to form proteins or can be broken up to create shorter polypeptide chains.  With the substrate bonded, the calmodulin chain wraps around the substrate to break it apart (See Figure 3)  All proteins can also be denatured, in which the chain of the protein stays intact but looses its structure.  These multiple structures makes Calmodulin an ideal protein for THz TDS measurements.

Figure 1

CaM- no binding ( 1CFD.pdb)     

Figure 2

CaM+Ca+2 (3CLN.pdb)  

Figure 3

CaM+Ca+2+TFP (1CTR.pdb)

For this research, the THz TDS measurements made with the lysozyme will be repeated with calmodulin.  Solutions for each of the three states of calmodulin will be prepared, as well as a denatured sample, and tested using florescence to confirm their structure.  The THz TDS technique will be used to measure characteristics of the sample.  The results of these measurements will definitively determine the contributions of protein structural vibrations to terahertz time domain spectroscopy response.