Lauren Matheson writes:
> From BIOSCI-REQUEST at net.bio.net Wed Jan 4 23:16:35 1995
> To: immunology at net.bio.net> From: Lauren Matheson <70214.1204 at compuserve.com>
> Subject: Antibody/Antigen Structure
> Date: 5 Jan 1995 04:38:59 GMT
> Message-ID: <3eft53$pkt$1 at mhade.production.compuserve.com>
>> Hi, I'm a grade 13 student in Toronto. I'm working on a project on Antibody
> and Antigen structure and interaction.
>> Questions: Are there mappings of the protein strands of IgG or others? If so
> where would they be found. How do antigens and antibodies fit together, is it
> just physical? How is a complete fit ensured? How do immune complexes change
$$$$$$$$$$$$$$$$
I think so, it is the thermodynamics and kinetics deterimine the affinity
(fit) of Ab to Ag. The complete fit is realized only when the intrisic
binding energy is maximized. The intrinsic binding energy, however, have
to be divided into forces for speed up (rate) the formation of the Ab-Ag
complex and the forces to stable the complex {affinity, [Ab-Ag]/([Ab][Ag])}
Four major forces are involved.
London disperse forces: like moon (Ag) and earth (Ab), can not be too close
and can not be too away. Moon and earth stick together as it is.
Hydrophorbic force: act like your ruber sticker on the glass wall. you squeeze
out of the air (water in term of Ab-Ag interaction) then the ruber is sucked
to the glass wall. Either the protein backbone has to bend (strain) Ag or
the Ag has to stess the Ab to squeeze off the associated water molecules on
the surface both of Ag and Ag binding sites of Ab. The loss of energy by
capture of Ag is profitable as more immobilized water molecules are released
as free form followed by release more energy in the system ( each Ag or Ab
molecule is surounded by more than one molecules of water. Experimental
evident: slight increase in size of Ag increases affinity.
Hydrogen and ionic bonding: act like your magnet sticker. Such forces
involve a certain weak or slight overlapping of electron orbitals between Ab
and Ag. Experimental evident: a ketone group (Ag=O:H-Ab) in
H
the Ag is replaced by a imine group (Ag=N:H-Ab) will have similar
H
affinity only at high pH (=N: is deprotonated and unpaired electrons
available for H-bonding) but the affinity of later is lost at low pH (pH<6)
H
due to the inability of forming H-bond (=NH+, charge prohibits H-bonding)
even though the size and shape of the two molecules are still very similar.
I hope my explanation is understandable
> the Fc regions of antibodies?
>> Your help would be greatly appreciated. Thank You.
> --
> Lauren Matheson 70214.1204 at compuserve.com>>
