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I would like to know the specific determinants for formation of IgG dimers. My understanding is the stem of the antibody is a homodimer of two heavy chains, covalently bonded through two disulfide bridges called the hinge region. Is there any association between the constant region? My reading would suggest no but I have not found a specific reference as such.

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Do you mean disulfides linking constant regions? – Alan Boyd May 2 '14 at 13:54
    
No, of course each immunoglubulin-like domain has an intramolecular disulfide (stabilizing the beta sandwich conformation). I mean between two heavy chain molecules. – user560 May 2 '14 at 13:56
up vote 1 down vote accepted

For human IgG1 and 4, the only inter-heavy chain disulfide bonds are the two in the hinge region. IgG2 has 4 disulfides in the hinge, and IgG3 has 11:

enter image description here

There are intra-heavy chain disulfides in the Fc region, and of course there are non-covalent bonds between the two heavy chains (as well as the light chains) to maintain structure, but aside from the hinge region the only other inter-chain disulfides are between heavy and light.

Here is an interesting review of classical (determined in the 1960s) and non-classical (more recently discovered) disulfide bond formation and structure in human IgGs.

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What's the nature of the hydrogen bonds/non-covalent bonding between two heavy chains? Are they naturally aggregated in the cell? – user560 May 2 '14 at 15:34
    
What do you mean by nature? This bonds are formed in the cell, yes, during the assembly of the antibody. – Chris May 2 '14 at 18:01

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