Protein Structure

Important Terms (Protein Structure)

Primary structure Linear sequence of amino acids in a polypeptide. Quaternary structure Arrangement of polypeptides in macromolecular assembly. Secondary structure A description of the three-dimensional structure adopted by a localized sections of the polypeptide chain. Tertiary structure A description of the arrangement of secondary structural elements within the protein. Units of length 1A = 0.1 […]

Protein Structure

PROTEINS are linear polymers of amino acids linked by amide bonds where the biological function is dictated by the sequence of amino acid residues within the polymer. Most proteins adopt a well-defined three-dimensional structure to fulfil their biological role. Thus, knowledge of protein structure is central to understanding the molecular basis of life.

INTRODUCTION (Protein Structure)

Proteins mediate the majority of biological processes. All proteins share the common feature that they are condensation polymers of amino acids whose sequence is specified by the genetic information contained within the genome of the organism. Complete DNA sequences for organisms ranging from Escherichia coli to humans suggest that the total number of proteins necessary […]

AMINO ACIDS (Protein Structure)

All proteins are synthesized from the 20 a-amino acids specified by the genetic code as shown in Fig. 1. The nature of an amino acid is determined by the "side-chain" attached to the a-carbon (Table I). All of these amino acids, except for glycine which carries two hydrogens on its a-carbon, have a chiral center […]

PROTEIN STRUCTURE DETERMINATION

A major requirement for understanding protein structure is a large database of three-dimensional structures. This is particularly important for the comparative method of structure prediction. Although considerable progress has been made in recent years toward establishment of a comprehensive structural database many more protein models are needed before structures can be predicted with a high […]

STRUCTURAL HIERACHY (Protein Structure)

The structure of a protein is generally understood in terms of an organizational hierarchy that consists of protein sequence, local secondary structure, tertiary structure, and finally quaternary structure. The study of protein structure in these terms has led to a greater understanding of the underlying physical principles that control the conformation and function of proteins. […]

SECONDARY STRUCTURAL MOTIFS (Protein Structure)

The major three-dimensional motifs found in proteins were predicted to exist by Cory and Pauling in 1951 before the first protein structure determination through their study of the structures of small peptides. They recognized that secondary structural motifs must accommodate the hydrogen bonding potential of the peptide bond as well as utilize the conformational angles […]

PROTEIN STABILITY (Protein Structure)

The term protein stability refers to the energy difference between the folded and unfolded state of the protein in solution. Remarkably, the free energy difference between these states is usually between 20 and 80 kJ/mol, which is of the magnitude of one to four hydrogen bonds. Although this suggests that proteins are only marginally stable, […]

TERTIARY STRUCTURE (Protein Structure)

A. Protein Folding Rules Examination of a large number of protein structures has yielded a few common rules about the folds that proteins can adopt as listed in the following. The theoretical basis for these features is not well understood, but most appear to result from the chirality of the amino acids, entropic considerations, and […]

MEMBRANE PROTEINS

Approximately one third of all proteins are tightly associated with membranes. These are much more difficult to crystallize or study by NMR than water-soluble proteins. As a consequence, there are far fewer structures of membrane proteins. Even so, those that have been determined provide insight into the manner in which polypep-tide chains interact with lipid […]

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