Sandbox 43
From Proteopedia
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[[Image:Alphalactalbumin secondary structure.gif]]<ref name="iv"> </ref> | [[Image:Alphalactalbumin secondary structure.gif]]<ref name="iv"> </ref> | ||
| - | α-lactalbumin is stabilized by four disulfide bonds and contains two structural domains. The α-domain is rich in α-helices and contains the Cys 6-Cys 120 and Cys 28-Cys 111 disulfide bond. The β-domain is rich in β-sheets and contains as Cys 61-Cys 77 and Cys 73-Cys 91 disulfide bonds.<ref name="iii">Tonya M. Hendrix, Yuri Griko, and Peter Privalov. 1996. Energetics of structural domains in a-lactalbumin. ''Protein Science'' 5923-931. </ref> | + | α-lactalbumin is stabilized by four disulfide bonds (yellow lines in picture above) and contains two structural domains. The α-domain is rich in α-helices and contains the Cys 6-Cys 120 and Cys 28-Cys 111 disulfide bond. The β-domain is rich in β-sheets and contains as Cys 61-Cys 77 and Cys 73-Cys 91 disulfide bonds.<ref name="iii">Tonya M. Hendrix, Yuri Griko, and Peter Privalov. 1996. Energetics of structural domains in a-lactalbumin. ''Protein Science'' 5923-931. </ref> |
== '''Metal Ions associated with α-lactalbumin'''== | == '''Metal Ions associated with α-lactalbumin'''== | ||
Revision as of 03:26, 20 September 2009
| Please do NOT make changes to this Sandbox. Sandboxes 30-60 are reserved for use by Biochemistry 410 & 412 at Messiah College taught by Dr. Hannah Tims during Fall 2012 and Spring 2013. |
Introduction to α-lactalbumin
α-lactalbumin is a 123 residue whey protein that is only found in milk and the mammary gland and is involved in production of lactose. α-lactalbumin is produced in the endoplasmic reticulum. When it makes it way to the Golgi it encounters galactosyltransferase and other substrates necessary for lactose synthesis.[1] The complex is made up of galactosyltransferase, α-lactalbumin, nucleotide substrate, and metal ion cofactors. α-lactalbumin is a modifier protein of the lactose synthetase complex.[2] Lactose synthetase catalyzes the final step in the biosynthesis of lactose in the mammary gland by the reaction:
UDP-D-galactose + D-glucose -- lactose + UDP.[3]
α-lactalbumin is highly similar to the c-type lysozymes sharing primary, secondary and tertiary structures. It is supposed that α-lactalbumin has evolved from c-type lysozyme, however the function of α-lactalbumin is distinct from c-type lysozyme.[2]
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| 1a4v, resolution 1.80Å () | |||||||||
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| Ligands: | |||||||||
| Activity: | Lactose synthase, with EC number 2.4.1.22 | ||||||||
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| Resources: | FirstGlance, OCA, PDBsum, RCSB | ||||||||
| Coordinates: | save as pdb, mmCIF, xml | ||||||||
Secondary and Tertiary Structure of α-lactalbumin
α-lactalbumin is composed of nine α-helices, eleven beta turns, two beta hairpin turns, and three strands. The three strands make up an antiparallel β-sheet, the nine helices are involved in 6 helix-helix interactions.[4] The primary structure can also been seen in the picture below.
Image:Alphalactalbumin secondary structure.gif[4]
α-lactalbumin is stabilized by four disulfide bonds (yellow lines in picture above) and contains two structural domains. The α-domain is rich in α-helices and contains the Cys 6-Cys 120 and Cys 28-Cys 111 disulfide bond. The β-domain is rich in β-sheets and contains as Cys 61-Cys 77 and Cys 73-Cys 91 disulfide bonds.[5]
Metal Ions associated with α-lactalbumin
α-lactalbumin is a small protein with calcium ions as cofactors. The binding of the calcium ion increases the stability of the protein in its native conformation and makes the folding of the protein much faster. The binding of the calcium ion acts of a nucleus for the stabilization of the tertiary structure in the protein, without it the process is much slower.[6] In α-lactalbumin native conformation the calcium ion is bound to a unique binding loop.[2] The calcium binding site is located in the β-domain and is formed by three Asp side chains and two mainchain carbonyls. This site the calcium ion has a pentagonal bypyramidal coordination.[4] [5] A secondary calcium binding site involves the residues Thr, Gln, Leu, and Asp. In this site the calcium ion has a tetrahedral coordination.[4] Protection from thermal, guanidine HCL and urea denaturation is provided by the stability given to the protein from the calcium ion binding. The calcium-binding site has also been shown to weakly bind Mg2+, Na2+, and K+ also. Removal of the calcium ion has shown to induce a conformational change. In the presence of denaturants or absence of calcium ions α-lactalbumin adopts the molten globule state and characterized by the conserved secondary structure but fluctuating tertiary structure.[2] α-lactalbumin, in its native state, possesses a relatively strong Zn2+ site causing subtle changes in α-lactalbumin structure upon binding to the calcium loaded protein. The Zn2+ is important in the binding of glucose in the lactose synthase complex.[2]
