Amino acids folding

Proteins are complex molecules that give cells structure and act as both enzymes and motors within cells. Proteins are long strings of amino acids folded in specific three-dimensional formations. There are twenty different animo acids in our bodies. DNA, the genetic material located in the cell nucleus, carries information for the order of the amino acids in each protein. Indeed, in the simplest sense, a gene is the... 

The hardness of only one type of protein crystal has been found in the literature. It is for lysozyme. This is an enzyme found in egg whites and tears. It destroys bacterial membranes. It is relatively small for a protein molecule, consisting of a chain of 129 amino acids folded into a globule with the volume = 30,000 A3. Its crystals are aggregates of these globular molecules held together by London forces (Stryer, 1988). 

CPMV particles have an icosahedral symmetry with a diameter of approximately 28 nm (Figure 9.2), the protein shell of the capsid is about 3.9nm thick [72], The structure of CPMV is known to near-atomic resolution (Figure 9.3) [73], The virions are formed by 60 copies of two different types of coat proteins, the small (S) subunit and the large (L) subunit. The S subunit (213 amino acids) folds into one jelly roll P-sandwich, and the L subunit (374 amino acids) folds into two jelly roll P-sandwich domains. The three domains form the asymmetric unit and are arranged in a similar surface lattice to T = 3 viruses, except they have different polypeptide sequences therefore the particle structure is described as a pseudo T = 3 or P = 3 symmetry [74]. 

MS channels are composed of amino acids, which are the building blocks of all proteins. The number of amino acids varies largely between different types of MS chaimels. For example, a single monomer of the bacterial chaimel MscL of E. coli is made of 136 amino acids folded in several a-helices connected by loops. A short N-terminal a-hetix of the MscL monomer is followed by two transmembrane helices TMl and TM2 and a C-terminal cytoplasmic a-helical domain (Fig. la). The TMl helix is connected to TM2 by a loop that extends into the pore region and hnes the periplasmic side of the channel. A 3-D structure of MscL obtained by X-ray crystallography has revealed that the chaimel folds as a homopentamer (Fig. la)... 

The carboxyl-terminal 469 amino acids of NompC resemble a class of ion channel proteins called TRP (transient receptor potential) channels. This region includes six putative transmembrane helices with a porelike region between the fifth and sixth helices. The amino-terminal 1150 amino acids consist almost exclusively of 29 ankyrin repeats (Figure 32.35). Ankyrin repeats are structural motifs formed by 33 amino acids folded into a hairpin loop followed by a helix-tum-helix. Importantly, in other proteins, regions with tandem arrays of these motifs mediate protein-protein interactions, suggesting that these arrays couple the motions of other proteins to the activity of the NompC channel. 

Rusticyanin s type 1 copper center with its ligands His 85, Cys 138, His 143, and Met 148 resembles those of the other small blue proteins. Although its tertiary structure is a /1-meander, there are distinct differences between the amino acid folding patterns of rusticyanin and the other small blue proteins. Plastocyanin contains 8 [22, 71], amicyanin 9 [20, 78], and rusticyanin 13 / -strands, respectively [112] (Fig. 16). 

Enzymes are catalysts that are found in living systems. They are globular proteins that is, they are polymers of amino acids folded to form a compact, roughly spherical shape. Within the enzyme are cavities containing active sites to which a substrate attaches and then undergoes chemical change. 

The 20 different amino acids in the linear polypeptide chain are the components that are arranged in a unique manner for each type of protein. If there are 200 or more amino acids, the number of different ways of linking these 20 amino acids, and hence of forming possible three-dimensional structures, is 200 . This means that this simple palette of amino acids leads to many possibilities for diversity in the protein itself, and that an almost infinite number of protein structures can be designed. I will describe in this chapter an example of how the long polypeptide chain of a protein consisting of many hundreds of amino acids folds in a totally unique manner to give a supermolecule with distinctive and well-controlled properties. 

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