Thesis final - after defense-7 - Jacobs University

Chapter 3
approximately 47%. The membrane proteins with the low polarity need detergents to be
separated from respective membranes due to hydrophobic interactions (117). However, in the
same study the polarity has not been correlated with the protein retention behavior in HIC.
The polarity values for the same protein on Grantham’s scale were almost one digit higher
than Zimmerman’s scale. This could be due to the different approaches used by the two
researchers while calculating the polarity indices for individual amino acids. It has been
reported that polar residues are normally located in the outer part of the protein while nonpolar
residues in the inner portion (117). The polarity of a protein has a direct relationship
with the number of polar residues (Asp, Asn, Glu, Lys, Arg and Gln) in the protein sequence.
An inverse relationship was reported between polarity and retention behavior of the proteins
(Figure 25 A-B). This revealed that the proteins with less polarity have a more non-polar
surface area and resulted in stronger binding to the HIC surface. In contrast, proteins with
high polarity had more polar and less non-polar surface area, resulting in less binding to
hydrophobic adsorbents and earlier elution during chromatography. This also ensured that
polarity has an inverse relationship with protein hydrophobicity.
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