Human beta two microglobulin: Difference between revisions

<StructureSection load='1dq8' size='500' side='right' caption='Crystal Structure of the Human Beta-2 Microglobulin (PDB entry [[1lds]])' scene=''>

[[Image:MHC Class 1.png|200px|left]]Human β2-Microglobulin is the non-covalently bound <scene name='Human_beta_two_microglobulin/Light_chain/2'>light chain</scene>

of the human class I  

typical properties of amyloid fibrils, principally in the joints and connective tissue.

The first crystal structure of Monomeric human b2m (Mhb2m) is solved in 2002 (pdb 1LDS). The protein is 99 residue in length and has a seven-stranded β sandwich fold typical of the Immunoglobulin superfamily. It is stabilized by a single disulfide bond between  

Cys-25 and Cys-80, which links the two β sheets.

Both of the two strucures adopt seven-stranded β sandwich fold with a short C' β strand located in the loop connecting strands C

and D. The most significant difference in the ctrystal structures of Mhb2m and MHCb2m involves residues in β strand D and the succeeding loop. When complexed with the MHC heavy chain, residues 50-56 of MHCb2m form two short β strands that separated by a two residue β bulge. These strands (depicted as D1 and D2 in Fig.1) each forms three main-chain-main-chain hydrogen bonds to the adjacent β strand E. The bulge in MHCb2m effectively twists the edge strand, which facilitate its binding to the surface of the heavy chain. However, this β bulge no longer exits in the crytal strucure of Mhb2m. The <scene name='Human_beta_two_microglobulin/D_strand/1'>conformation of D strand </scene>in Mhb2m provides an ideal assembly surface, making this edge-strand pair vulnerable to aggregation. The hydrogen-bonding potential of strand D is satisfied by the formation intermolecular interactionswith adjecent molecules, demonstrating the potential for this region to propagate assembly through edge-strand interactions.