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

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

Document<br />

Figure 6<br />

Stereo diagram of the NMR solution structure of the tick anticoagulant peptide. The crucial<br />

N-terminus Arg 3 is indicated along with the pattern of cysteine bonds.<br />

Page 273<br />

mined <strong>by</strong> 2D-NMR studies [57,58] (Figure 6). With the exception of the region neighboring the<br />

Cys 15—Cys 39 bond in TAP, these studies support the originally proposed idea that there are significant<br />

structural similarities between TAP and Kunitz proteinase inhibitors [10]. Nevertheless, it is clear that<br />

TAP inhibitors FXa <strong>by</strong> a fundamentally different, and as yet, not fully understood mechanism.<br />

D. AcAP's<br />

In addition to ticks and leeches, other hematophagous organisms such as hook- worms have also evolved<br />

potent and selective Factor Xa inhibitors as anticoagulant strategies. Two such proteins, AcAP5 and<br />

AcAP6, have been isolated from the Ancylostoma caninum hookworm [19]. The AcAP5 protein is a 77amino-acid<br />

polypeptide with 10 cysteine residues. It inhibits the amidolytic activity of Factor Xa with a<br />

K i of 43 ± 5 pM. Incubation of rAcAP5 with its target enzyme Factor Xa results in partial cleavage of<br />

the Arg 40–Gly 41 peptide bond suggesting the sequence around this cleavage site can adopt the restricted<br />

conformational requirements of substrates [47].<br />

The AcAP6 protein is a 75-amino-acid polypeptide, also with cysteines, with a K i for Factor Xa<br />

inhibition of 996 ± 65 pM. Alignment of the sequences of AcAP5 and AcAP6 suggest the P1 residue in<br />

AcAP6 is Phe 38 and not the basic residue usually associated with Factor Xa specificity [19]. Substitution<br />

of Phe 38 in AcAP6 with Arg resulted in a mutant that inhibited Factor Xa with a potency similar to<br />

rAcAP5. Both AcAP6 and ecotin suggest that an Arg or<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_273.html (1 of 2) [4/5/2004 5:13:03 PM]

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

Saved successfully!

Ooh no, something went wrong!