Protein Secondary Structure:- Common Secondary Structures Have Characteristic Bond Angles and Amino Acid Content

The helix and the conformation are the major repetitive secondary structures in a wide variety of proteins, although other repetitive structures do exist in some specialized proteins (an example is collagen; see Fig. 4–13 on page 128). Every type of secondary structure can be completely described by the bond angles ϕ and ψ at each residue. As shown by a Ramachandran plot, the α helix and conformation fall within a relatively restricted range of sterically allowed structures (Fig. 4–9a). Most values of and taken from known protein structures fall into the expected regions, with high concentrations near the α helix and β conformation values as predicted (Fig. 4–9b). The only amino acid residue often found in a conformation outside these regions is glycine. Because its side chain, a single hydrogen atom, is small, a Gly residue can take part in many conformations that are sterically forbidden for other amino acids. Some amino acids are accommodated better than others in the different types of secondary structures. An overall summary is presented in Figure 4–10. Some

FIGURE 4–9 Ramachandran plots for a variety of structures. (a) The values of ϕ for ψ various allowed secondary structures are over laid on the plot from Figure 4–3. Although left-handed helices ex tending over several amino acid residues are theoretically possible, they have not been observed in proteins. (b) The values of ϕ

and ψ for all the amino acid residues except Gly in the enzyme pyruvate ki nase (isolated from rabbit) are overlaid on the plot of theoretically allowed conformations (Fig. 4–3). The small, flexible Gly residues were excluded because they frequently fall outside the expected ranges (blue).

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مواضيع ذات صلة

Protein Tertiary and Quaternary Structures: -Fibrous Proteins Are Adapted for a Structural Function

Protein Secondary Structure:- β Turns Are Common in Proteins

Protein Secondary Structure:- Amino Acid Sequence Affects α Helix Stability

Overview of Protein Structure:- The Peptide Bond Is Rigid and Planar

Overview of Protein Structure:- A Protein’s Conformation Is Stabilized Largely by Weak Interactions

Overview of Protein Structure:- The Peptide Bond Is Rigid and Planar

Overview of Protein Structure:- A Protein’s Conformation Is Stabilized Largely by Weak Interactions

Protein Sequences and Evolution:- Protein Sequences Can Elucidate the History of Life on Earth

The Covalent Structure of Proteins:- Amino Acid Sequences Provide Important Biochemical Information

The Covalent Structure of Proteins:- Small Peptides and Proteins Can Be Chemically Synthesized

The Covalent Structure of Proteins:- Amino Acid Sequences Can Also Be Deduced by Other Methods

The Covalent Structure of Proteins:-Large Proteins Must Be Sequenced in Smaller Segments