10.12.2012 Views

netLibrary - eBook Summary Structure-based Drug Design by ...

netLibrary - eBook Summary Structure-based Drug Design by ...

netLibrary - eBook Summary Structure-based Drug Design by ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Document<br />

has a single membrane-spanning region and a cytoplasmic region of 213 amino acids. The IL-1RII<br />

receptor has a single membrane-spanning region and a cytoplasmic region of 29 amino acids.<br />

Page 401<br />

All three IL-1 molecules bind with a high affinity to the receptor IL-1RI. However only IL-1α and IL-<br />

1β produce a detectable response [29]. The IL-1Ra molecule completely blocks the binding of the<br />

former two molecules without inducing any signal transduction events. The second IL-1 receptor, IL-<br />

1RII, similarly binds IL-1 tightly but does not produce any signal [30]. The soluble portion of IL-1RI<br />

binds to IL-1Ra, IL-1α, and IL-1β in decreasing order of affinity whereas the soluble portion of IL-1RII<br />

binds IL-1β, proIL-1β, IL-1α, and IL-1Ra, in that order. It therefore appears that both IL-1Ra and IL-<br />

1RII take part in modulation of the agonist molecules, an argument supported <strong>by</strong> the finding that soluble<br />

IL-1RII binds IL-1β with a similar affinity to the cell-associated receptor; whereas, the affinity of IL-<br />

1Ra to such a soluble receptor is some 2000 times less [31,32,33]. Greenfeder, et al., [18] have<br />

identified a new molecule, the IL-1 accessory protein IL-1RacP. The complex of IL-1 and IL-1 receptor<br />

binds to IL-1RacP and together they induce the signal [18]. Greenfeder also observed that antibodies to<br />

IL-1RI and to IL-1RacP block IL-1 binding and activity. From sequence analysis it appears that the<br />

cytoplasmic domains of IL-1R and IL-1RacP contain the same amino acid domains commonly found in<br />

the members of the GTPase family of proteins [34]. It has been proposed that such a complexation may<br />

lead to a closer proximity of these cytoplasmic domains and thus facilitate signal transduction. A scheme<br />

showing functional relationships between molecules that make up the IL-1 system—IL-1α, IL-1β, IL-<br />

1Ra, IL-1RI, IL-1RII, and related receptors—is shown in Figure 1.<br />

C. Autoantibodies of IL-1<br />

In addition to these molecules, naturally occurring neutralizing autoantibodies of IgG type to IL-1α have<br />

been identified. These have been detected in serum isolated from human donors. [35,36]. These<br />

antibodies bind to both proIL-1α and 17-kDa IL-1α [37] and completely prevent the binding of IL-1α to<br />

type-I cell surface receptors [38]. Patients with autoimmune diseases have higher populations of these<br />

antibodies [39].<br />

III. Three-Dimensional Structural Information<br />

In an effort to understand the natural and interactions of the IL-1 family, various laboratories have<br />

undertaken the task of elucidating the three-dimensional structure of the molecules. To the present this<br />

has resulted in the structures of all three members of the IL-1 family being solved independently <strong>by</strong> both<br />

x-ray<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_401.html [4/5/2004 5:44:16 PM]

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!