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 />

Table 2 RMS Distance of Aligned Cα Moieties of the Three Interleukin-1 <strong>Structure</strong>s<br />

IL-1β IL-1α IL-1Ra<br />

IL-1β 0.0 1.8 Å (36.3%) 1.42 Å (30.7%)<br />

IL-1α 1.8 Å (36.3%) 0.0 1.8 Å (27.5%)<br />

IL-1Ra 1.42 Å (30.7%) 1.8 Å (27.5%) 0.0<br />

Number in parentheses referred to sequence identities between the aligned structures.<br />

A. Expression and Processing of IL-1<br />

Page 399<br />

All three IL-1 molecules, IL-1α, IL-1β, and IL-1Ra are synthesized as 31 kDa precursor molecules<br />

produced primarily <strong>by</strong> mononuclear phagocytes. These precursor proteins can be subsequently<br />

processed to mature 17 kDa molecules. The means where<strong>by</strong> this is achieved appears to be different for<br />

each type of molecule and may help to explain the roles of the three. Both agonist molecules IL-1α and<br />

IL-1β lack a classical hydrophobic leader sequence and thus must be processed in an alternative way.<br />

The two can be separated <strong>by</strong> their biological activity in the precursor form, IL-1α being active in both<br />

precursor and mature forms while IL-1β produces a biological response only in its processed form. In<br />

addition, a specific enzyme, Interleukin-1 beta converting enzyme (ICE), cleaves IL-1β to its mature<br />

form. This enzyme is a cysteine protease whose only known substrate is proIL-1β, which it cleaves at<br />

Ala 117 [19,20]. The means where<strong>by</strong> pro IL-1α is processed is still largely a mystery although it has<br />

been postulated that a calpain or related protein may perform the task.<br />

Naturally occurring IL-1Ra is a 22 kDa glycosylated protein [14,15,21– 24] that possesses a signal<br />

sequence. It is likely that it is processed in the conventional manner as can be concluded <strong>by</strong> the<br />

glycosylation states of the molecule not present in the agonists [25]. The LPS-stimulated human blood<br />

monocytes initially express the gene for IL-1Ra [25]. An alternatively spliced form of IL-1Ra also exists<br />

(intracellular IL-1Ra), which remains inside the cell presumably to block intracellular IL-1 action [26].<br />

Both soluble and intracellular forms of IL-1Ra block IL-1R but do not trigger any biological response.<br />

B. Receptors and Responses<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_399.html (1 of 2) [4/5/2004 5:44:09 PM]

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

Saved successfully!

Ooh no, something went wrong!