C

FIGURE 5*11 p sheets twist in a right-handed manner along their length.

The schematic shows the mixed sttucture of the E cob proles thionedoxin. (j grands are drawn, as arrows Irom the amino to the carboxyl end of the protein (Source: Adapted (torn Bran den C. and Tdoie i. 1999 Introduction to protein structure, 2nd edition, p 20, fig 2.7a.)

FIGURE 5-12 Regular and irregular features of protein structures, irregular configurations tn the backbone (green) allow the rnaximurn formation of secondary structure^ (ft sheet tn purple and a helix in turquoise) by other regions of tine protein The structure shown is that ol the E1 protein ol adenovirus (Enernark EJ„ Chen G„ Vaughn D.E., Stenfund A„ .ind Joshoa Tor L 2000. Mol Cell 6; 149.) Image prepared wtth MoiSciipt. BobSrript, and Rastei 3D

FIGURE 5-12 Regular and irregular features of protein structures, irregular configurations tn the backbone (green) allow the rnaximurn formation of secondary structure^ (ft sheet tn purple and a helix in turquoise) by other regions of tine protein The structure shown is that ol the E1 protein ol adenovirus (Enernark EJ„ Chen G„ Vaughn D.E., Stenfund A„ .ind Joshoa Tor L 2000. Mol Cell 6; 149.) Image prepared wtth MoiSciipt. BobSrript, and Rastei 3D

shapes. The three-dimensional structures of the polypeptide chains of proteins are thus compromises between the tendency of the backbones to form either « helices or |3 sheets and the tendency of the side groups to twist the backbone into less regular configurations that maximize the strength of the secondary bonds formed by those side groups (Figure 5-12).

As we discuss in more detail below, one of the strongest influences on protein folding can be attributed to the burial of hydrophobic (nonpolar) amino acid side groups into the core of the protein's structure. This leads to the prediction that in aqueous solutions, proteins containing very large numbers of nonpolar side groups will tend to internalize the nonpolar residues and be more stable than proteins containing mostly polar groups. If we disrupt a polar molecule held together by a large number of internal hydrogen bonds, the decrease in free energy is often small since the polar groups can then hydrogen-bond to water instead. On the other hand, when we disrupt molecules having many nonpolar groups, there is usually a much greater loss in free energy because the disruption necessarily inserts nnnpolar groups into water.

0 0

Post a comment