Complement??

David L. Haviland, Ph.D. dhavilan at IMM2.IMM.UTH.TMC.EDU
Fri Jan 3 11:14:47 EST 1997


At 16:45 1/2/97 -0800, Kenneth T. Miyasaki DDS PhD wrote:
>Complement (C) is a component of the immune system formed by an
>interacting network of plasma glycoproteins and cell receptors. The

Though noble, you have saved the individual who posed the question the
library time he needed to answer the question himself... ;-)

>Components of the 
>Membrane Attack Complex
>	C5 (encoded on chromosome 9q34.1) is a 191 kdal heterodimeric protein
>consisting of one115 kdal and one 75 kdal subunit. Cleavage of the
>larger subunit by the C5 convertase results in the formation of a 11.2
>kdal C5a chemoattractant molecule and 180 kdal C5b. C5 is structurally
>related to C3 and C4, and has the internal thioester bond that dominates
>the behavior of these molecules.

As Ken obtained and posted this summary of complement, he is not the
author, so I do not blame him for errors in this article.  I do, however,
suggest the author, whomever that may be, revise this summary.  

True, C3,C4, & C5 are conserved in amino acid sequences and share similar
gene structural organization.  However, the last sentence is simply wrong,
plain and simple.   C5 *never* did, nor does it currently have a thioester
bond.  The future is up to evolution.  Only C3 and C4  (and
alpha-2-macroglobulin) possess this unique chemistry.  C5 does have the
critical Cys residue for thioester bond formation, while a2M, C3, and  C4 do.

David

=============================
 David L. Haviland, Ph.D.
 Asst. Prof. Immunology 
 University of Texas - Houston, H.S.C.
 Institute of Molecular Medicine  
 2121 W. Holcombe Blvd.  
 Houston, TX  77030 
 Internet:"dhavilan at imm2.imm.uth.tmc.edu" 
 Voice: 713.500.2413  FAX: 713.500.2424
 ------------------------------------------------------  
" Sometimes you're the windsheild, sometimes you're the bug."
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