An example of the globin fold, the oxygen-carrying protein myoglobin (PDB ID 1MBA) from the mollusc Aplysia limacina.

The globin fold is a common three-dimensional fold in proteins. This fold typically consists of eight alpha helices, although some proteins have additional helix extensions at their termini. The globin fold is found in its namesake proteins hemoglobin and myoglobin as well as in phycocyanin proteins. Because myoglobin was the first protein whose structure was solved, the globin fold was thus the first protein fold discovered. Since the globin fold contains only helices, it is classified as an all-alpha protein fold. General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance transparent (gas) very pale blue (liquid) Atomic mass 15. ... Myoglobin is a single-chain protein of 153 amino acids, containing a heme (iron-containing porphyrin) group in the center. ... Classes Caudofoveata Aplacophora Polyplacophora - Chitons Monoplacophora Bivalvia - Bivalves Scaphopoda - Tusk shells Gastropoda - Snails and Slugs Cephalopoda - Squids, Octopuses, etc. ... In biochemistry, the tertiary structure of a protein is its overall shape. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... A diagram of the alpha helix structure of amino acids In proteins, the α helix is a major structural motif in secondary structure. ... 3-dimensional structure of hemoglobin. ... Myoglobin is a single-chain protein of 153 amino acids, containing a heme (iron-containing porphyrin) group in the center. ... Phycocyanin is a pigment that is blue and is readily found in blue-green algae. ...

Helix packing

The eight helices of the globin fold core share significant nonlocal structure, unlike other structural motifs in which amino acids close to each other in primary sequence are also close in space. The helices pack together at an average angle of about 50 degrees, significantly steeper than other helical packings such as the helix bundle. The exact angle of helix packing depends on the sequence of the protein, because packing is mediated by the sterics and hydrophobic interactions of the amino acid side chains near the helix interfaces. It has been suggested that Supersecondary structure be merged into this article or section. ... An amino acid residue is what is left of an amino acid once a molecule of water has been lost (an H+ from the nitrogenous side and an OH- from the carboxylic side) in the formation of a peptide bond. ... Steric effects are the interaction of molecules dictated by their shape and/or spatial relationships. ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ... The term Side chain can have different meanings depending on the context: In chemistry and biochemistry a side chain is a part of a molecule attached to a core structure. ...

Sequence conservation

Although the globin fold is highly evolutionarily conserved, the sequences that form the fold can have as low as 16% sequence identity. While the sequence specificity of the fold is not stringent, the hydrophobic core of the protein must be maintained and hydrophobic patches on the generally hydrophilic solvent-exposed surface must be avoided in order for the structure to remain stable and soluble. The most famous mutation in the globin fold is a change from glutamate to valine in one chain of the hemoglobin molecule. This mutation creates a "hydrophobic patch" on the protein surface that promotes intermolecular aggregation, the molecular event that gives rise to sickle-cell anemia. A hypothetical phylogenetic tree of all extant organisms, based on 16S rRNA gene sequence data, showing the evolutionary history of the three domains of life, bacteria, archaea and eukaryotes. ... The hydrophobic effect is the property that nonpolar molecules like to self-associate in the presence of aqueous solution. ... The adjective hydrophilic describes something that likes water (from Greek hydros = water; philos = friend). ... It has been suggested that this article or section be merged with Solution. ... Glutamate is the anion of glutamic acid. ... Valine is one of the 20 natural amino acids, and is coded for in DNA. Nutritionally, valine is also an essential amino acid. ... Sickle-shaped red blood cells Sickle-cell anemia or anaemia (also sickle-cell disease) is a genetic disorder in which red blood cells may change shape under certain circumstances. ...

References

• Branden C, Tooze J. (1999). Introduction to Protein Structure 2nd ed. Garland Publishing: New York, NY.

External links

• SCOP globin folds

In biochemistry, the tertiary structure of a protein is its overall shape. ... Within a protein, a structural domain (domain) is an element of overall structure that is self-stabilizing and often folds independently of the rest of the protein chain. ... Protein folding is the process by which a protein structure assumes its functional shape or conformation. ... Example of an immunoglobulin domain, the fibronectin type III domain from human tenascin (PDB accesion code 1TEN), colored from blue (N-terminus) to red (C-terminus). ... Top view of a triosephosphateisomerase (TIM) barrel (PDB accession code 8TIM), colored from blue (N-terminus) to red (C-terminus). ... Ribbon diagram of the SH2 domain of human P56-Lck tyrosine kinase (PDB accession code 1LKK, chain A), colored from blue (N-terminus) to red (C-terminus). ... A conotoxin is one of a group of neurotoxic peptides isolated from the venom of the marine cone snail. ...