Chemistry: natural resins or derivatives; peptides or proteins; – Proteins – i.e. – more than 100 amino acid residues
Reexamination Certificate
1999-07-08
2001-02-20
Slobodyansky, Elizabeth (Department: 1652)
Chemistry: natural resins or derivatives; peptides or proteins;
Proteins, i.e., more than 100 amino acid residues
C530S324000, C530S325000, C530S326000, C530S387300, C435S212000
Reexamination Certificate
active
06191260
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel human gene encoding a polypeptide expressed in human brain tissue which is a member of the serine protease inhibitor (“serpin”) superfamily and appears to be a human homolog of “neuroserpin,” a serpin recently identified in the chicken. More specifically, isolated nucleic acid molecules are provided encoding a human polypeptide named Brain-Associated Inhibitor of Tissue-Type Plasminogen Activator, hereinafter referred to as “BAIT.” BAIT polypeptides are also provided, as are vectors, host cells and recombinant methods for producing the same. The invention further relates to screening methods for identifying agonists and antagonists of BAIT activity. Also provided are diagnostic methods for detecting disorders related to the central and peripheral nervous system and the circulatory system, and therapeutic methods for treating such disorders.
BACKGROUND OF THE INVENTION
Localized proteolytic activity through the action of proteases plays a critical regulatory role in a variety of important biological processes. For instance, the enzyme plasmin plays such a role in hemostasis, angiogenesis, tumor metastisis, cellular migration and ovulation. Plasmin is generated from its precursor zymogen plasminogen by the action of plasminogen activators (PAs) such as tissue-type PA (t-PA) and urokinase-type (u-PA), both of which are serine proteases. The activity of the PA system is precisely regulated by several mechanisms, one of which involves the interaction of t-PA and u-PA with specific plasminogen activator inhibitors. Among these serine protease inhibitors (i.e., serpins), plasminogen activator inhibitor type 1 (PAI-1) is unique in its ability to efficiently inhibit u-PA as well as the single and two-chain forms of t-PA. High PAI-1 levels are associated with an increased risk of thromboembolic disease, while PAI-1 deficiency may represent an inherited autosomal recessive bleeding disorder. See, for instance, Reilly, T. M., et al., Recombinant plasminogen activator inhibitor type 1: a review of structural, functional, and biological aspects,
Blood Coag. And Fibrinolysis
5:73-81 (1994).
Serpin Mechanism
The serpins are a gene family that encompasses a wide variety of protein products, including many of the proteinase inhibitors in plasma (Huber & Carrell, 1989; full citations of references cited in this section on Serpin Mechanism are listed at the end of this section). However, in spite of their name, not all serpins are proteinase inhibitors. They include steroid binding globulins, the prohormone angiotensinogen, the egg white protein ovalbumin, and barley protein Z, a major constituent of beer. The serpins are thought to share a common tertiary structure (Doolittle. 1983) and to have evolved from a common ancestor (Hunt & Dayhoff. 1980). Proteins with recognizable sequence homology have been identified in vertebrates, plants, insects and viruses but not, thus far, in prokaryotes (Huber & Carrell. 1989; Sasaki. 1991; Komiyama, Ray, Pickup, et al. 1994). Current models of serpin structure are based largely on seminal X-ray crystallographic studies of one member of the family, &agr;-1-antitrypsin (&agr;1AT), also called &agr;-1-proteinase inhibitor (Huber & Carrell. 1989). The structure of a modified form of &agr;1AT, cleaved in its reactive center, was solved by Loebermann and coworkers in 1984 (Loebermann, Tokuoka, Deisenhofer, & Huber. 1984). An interesting feature of this structure was that the two residues normally comprising the reactive center (Met-Ser), were found on opposite ends of the molecule, separated by almost 70 Å. Loebermann and coworkers proposed that a relaxation of a strained configuration takes place upon cleavage of the reactive center peptide bond, rather than a major rearrangement of the inhibitor structure. In this model, the native reactive center is part of an exposed loop, also called the strained loop (Loebermann, Tokuoka, Deisenhofer, & Huber. 1984; Carrell & Boswell. 1986; Sprang. 1992). Upon cleavage, this loop moves or “snaps back”, becoming one of the central strands in a major &bgr;-sheet structure (&bgr;-sheet A). This transformation is accompanied by a large increase in thermal stability (Carrell & Owen. 1985; Gettins & Harten. 1988; Bruch, Weiss, & Engel. 1988; Lawrence, Olson, Palaniappan, & Ginsburg. 1994b).
Recent crystallographic structures of several native serpins, with intact reactive center loops, have confirmed Loebermann's hypothesis that the overall native serpin structure is very similar to cleaved &agr;1AT, but that the reactive center loop is exposed above the plane of the molecule (Schreuder, de Boer, Dijkema, et al. 1994; Carrell, Stein, Fermi, & Wardell. 1994; Stein, Leslie, Finch, Turnell, McLaughlin, & Carrell. 1990; Wei, Rubin, Cooperman, & Christianson. 1994). Additional evidence for this model has come from studies where synthetic peptides, homologous to the reactive center loops of &agr;1AT, antithrombin III (ATIII), or PAI-1 when added in trans, incorporate into their respective molecules, presumably as a central strand of &bgr;-sheet A (Björk, Ylinenjärvi, Olson, & Bock. 1992; Björk, Nordling, Larsson, & Olson. 1992; Schulze, Baumann, Knof, Jaeger, Huber, &. Laurell. 1990; Carrell, Evans, & Stein. 1991; Kvassman, Lawrence, & Shore. 1995). This leads to an increase in thermal stability similar to that observed following cleavage of a serpin at its reactive center, and converts the serpin from an inhibitor to a substrate for its target proteinase. A third serpin structural form has also been identified, the so-called latent conformation. In this structure the reactive center loop is intact, but instead of being exposed, the entire amiino-terminal side of the reactive center loop is inserted as the central strand into &bgr;-sheet A (Mottonen, Strand, Symersky, et al. 1992). This accounts for the increased stability of latent PAI-1 (Lawrence, Olson, Palaniappan, & Ginsburg. 1994a) as well as its lack of inhibitory activity (Hekman & Loskutoff. 1985). The ability to adopt this conformation is not unique to PAI-1, but has also now been shown for ATIII and &agr;1AT (Carrell, Stein, Fermi, & Wardell. 1994; Lomas, Elliot, Chang, Wardell, & Carrell. 1995). Together, these data have led to the hypothesis that active serpins have mobile reactive center loops, and that this mobility is essential for inhibitor function (Lawrence, Strandberg, Ericson, & Ny. 1990; Carrell, Evans, & Stein. 1991; Carrell & Evans. 1992; Lawrence, Olson, Palaniappan, & Ginsburg. 1994b; Shore, Day, Francis-Chmura, et al. 1994; Lawrence, Ginsburg, Day, et al. 1995; Fa, Karolin, Aleshkov, Strandberg, Johansson, & Ny. 1995; Olson, Bock, Kvassman, et al. 1995). The large increase in thermal stability observed with loop insertion, is presumably due to reorganization of the five stranded &bgr;-sheet A from a mixed parallel-antiparallel arrangement to a six stranded, predominantly antiparallel &bgr;-sheet (Carrell & Owen. 1985; Gettins & Harten. 1988; Bruch, Weiss, & Engel. 1988; Lawrence, Olson, Palaniappan, & Ginsburg. 1994a). This dramatic stabilization has led to the suggestion that native inhibitory serpins may be metastable structures, kinetically trapped in a state of higher free energy than their most stable thermodynamic state (Lawrence, Ginsburg, Day, et al. 1995; Lee, Park, & Yu. 1996). Such an energetically unfavorable structure would almost certainly be subject to negative selection, and thus its retention in all inhibitory serpins implies that it has been conserved for functional reasons.
The serpins act as “suicide inhibitors” that react only once with a target proteinase forming an SDS-stable complex. They interact by presenting a “bait” amino acid residue, in their reactive center, to the enzyme. This bait residue is thought to mimic the normal substrate of the enzyme and to associate with the specificity crevice, or S1 site, of the enzyme (Carrell & Boswell. 1986; Huber & Carrell. 1989; Bode & Huber. 1994). The bait amino acid is called the P1 residue, with the amino acids to
Coleman Timothy A.
Dillon Patrick J.
Hastings Gregg A.
Lawrence Daniel A.
American Red Cross
Human Genome Sciences Inc.
Slobodyansky Elizabeth
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