The Three-Dimensional Structure of Proteins

The Three-Dimensional Structure of Proteins

The covalent structure of a protein is composed of hundreds of individual bonds. Because free rotation is possible around a good portion of these bonds, there are a very high number of possible conformations the protein can assume. However, each protein is responsible for a particular chemical or structural function, signifying that each one has a distinctive three-dimensional configuration. By the early 1900’s, numerous proteins had been crystallized. Because the ordered collection of molecules in a crystal can only form if all of the molecular units are the same, the discovery that proteins could be crystallized proved that even large proteins have distinct chemical structures. This deduction completely transformed the understanding of proteins and their respective functions. It is important to investigate how a series of amino acids in a polypeptide chain is translated into a three-dimensional protein structure. There are five general topics related to this process: the structure of a protein is determined by its amino acid sequence, the role of a protein is dependent on its unique structure, an isolated protein typically exists in a small number of stable forms, non-covalent interactions are the most important stabilizing forces in a protein structure, and there are structural patterns that aid in explaining and understanding protein architecture.

The conformation of a protein is the three-dimensional arrangement of its atoms. The achievable conformations of a protein include all structural states that can be made without breaking any covalent bonds. A conformational change could happen, for instance, by rotation around a single bond. Of the numerous conformations possible (the...

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...s remain the same through the entire segment. A few types of secondary structures are especially stable and thus occur widely in proteins. The most prominent of the secondary structures are the alpha helix and beta conformations, as well as a structure called a beta turn. When a regular pattern cannot be determined or found, the secondary structure of the protein is understandably referred to as undefined or even a random coil. However, the path of a polypeptide backbone is anything but random; it is generally unchanging and specific to the function and structure of that specific protein. The simplest arrangement any polypeptide chain can undertake is a helical structure, also known as an alpha helix. This particular structure can be described as the polypeptide backbone tightly wound about an imaginary axis with the R groups of the amino acid protruding outwards.