Ask A Scientist Molecular Biology Archive

name         Amanda
status       student
age          16

Question -   What are homodimeric glycoproteins?
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Amanda, 

If we break down the fancy words, the meaning becomes clear. A dimer is something 
made up of two subunits (a trimer is made up of three subunits, a monomer has one subunit). 
So a dimeric protein is made up of two individual protein chains. Now, you could have 
two of the same thing, say, A and A, or you could have two different subunits, say, 
A and B. "Homo" means the same, so a homodimeric protein is made up of two identical 
subunits. If it was made up of A and B, it would be a "heterodimer" or heterodimeric 
protein.

All that leaves is the "glyco" part. "Glyco-" means "sugar" in biology. Many proteins are 
modified after they are made. One of the most common modifications is to have one or more 
short chains of sugars attached to the proteins at certain, specific places in the protein.

So.... a homodimeric glycoprotein is a protein made up of two identical (protein) subunits, 
with the protein chains modified by having sugar chains on them. Incidentally, glycosylated 
proteins (i.e., glycoproteins, or proteins modified with sugar chains) and are usually 
either present on the cell surface, or they are secreted. In other words, the vast 
majority of proteins inside a human cell are not glycosylated, while the majority of 
proteins that are secreted are glycosylated.

An example of a homodimeric glycoprotein in your body would be an antibody molecule. Two 
identical chains of "IgG" are made and brought together inside the cell, modified with 
sugar chains, and secreted as one large assembly.

Paul Mahoney, Ph.D
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Homo....same
dimer...two parts...as apposed to a monomeric glycoprotein which has only one part.  
Ergo...two parts that are the same that make up the glycoprotein.

Peter Faletra
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Two of the same sugar coated polypeptides in one protein
homo--same
dimer-two
glyco-sugar
protein

Jeannine M. Durdik
Associate Professor of Biological Sciences
Fayetteville AR 72701
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Dear Amanda,

Dimeric proteins are those that have 2 "subunits".  This means that they are actually 2 
separate protein molecules, also known as "polypeptides", held together as a single, 
dimeric protein by either hydrogen bonding, ionic (charged) interactions, actual 
covalent disulfide bonding, or some combination of these interactions.

In a homodimeric protein, both of these 2 subunits would actually be the same polypeptide, 
held together by the above interactions.  In heterodimers, the 2 subunits would be different 
polypeptides.

Glycoproteins are those that have been modified after their synthesis by the attachment of 
1 or more polysaccharide prosthetic groups, which are often quite large with branching side 
chains.

So a homodimeric glycoprotein would consist of 2 identical polysaccharide-conjugated 
polypeptide subunits, bonded together as a single, functional protein.

I hope that this is understandable & helpful for you,

Jeff Buzby, Ph.D.
CHOC Research Institute

NEWTON AAS
Division of Educational Programs
Argonne National Laboratory
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