Proteins Bowman-Birk protease inhibitor

Legume (Fabaceae) Bowman-Birk protease inhibitor proteins (BBPIPs) are typically double-headed protease inhibitors with 14 cysteines (i.e. 7 S-S links) and molecular masses of 7-9 kDa. All the BBPIPs listed were isolated from seeds except for the Medicago sativa (alfalfa) leaf BBPIPs. For other details see the legend to Table 4. 

Plant species (common name) Bowman-Birk protease inhibitor proteins Protease specificity (IC50) fKd, Kil (reactive site) Ref. 

Angiotensin I converting enzyme Acquired immunodeficiency syndrome Aspartic protease inhibitor Bowman Birk protease inhibitor protein Chymotrypsin Cysteine protease inhibitor Endothelin-converting enzyme Elastase... 

Collier K, Vogtentanz G, Amin A, Estabrook M, Estell D, Fox B, Power S, Rao R, Schmidt B. (2009) Generation and identification of variants with improved purification yield of Bowman-Birk protease inhibitors carrying protein binding loops. Protein Expr Purif, 68, 146-160. 

The Bowman-Birk type protease inhibitors represent a class of low molecular weight, cysteine-rich proteins found in legume seeds (.10). The major Bowman-Birk inhibitor in soybean seeds is a double-headed protein capable of blocking the activity of both trypsin and chymotrypsin. This protein represents approximately 4% of the total protein in soybean seeds (1J ). In contrast to the soybean trypsin inhibitor (Kunitz), the "double-headed inhibitor (referred to as BB) is typical of protease inhibitors present in a large number of legume seeds for example, peanuts (12) chick peas (33)5 kidney beans (3JO adzuki beans (33) lima beans (16). 

The most thoroughly studied mechanism of protein protease inhibitors is that of the standard mechanism (or Canonical or Laskowski mechanism) inhibitors of serine proteases (1) (Fig. 2). Standard mechanism inhibitors include the Kazal, Kunitz, and Bowman-Birk family of inhibitors and bind in a lock-and-key fashion. Ah standard mechanism inhibitors insert a reactive loop into the active site of the protease, which is complementary to the substrate specificity of the target protease and binds in an extended fi-sheet with the enzyme in a substrate-like manner. WhUe bound to the protease, the scissile bond of standard mechaiusm inhibitors is hydrolyzed very slowly, but products are not released and the amide bond is re-ligated. The standard mechanism is an efficient way to inhibit serine proteases, and it is thus used by many structurally... 

TIs are protease-inhibiting factors that bind the protease enzymes to decrease their catalytic power. The two predominant protease inhibitors are Kunitz trypsin inhibitor and Bowman-Birk inhibitor (BBI), and they are both protein in nature. 

Protease inhibitors in soybeans, known as trypsin inhibitors (TIs), play important roles in nutritional properties of soybeans and soy protein products. Two types of TI are the Kunitz inhibitor and the Bowman-Birk inhibitor. The Kunitz inhibitor has a MW of 21,500 with two disulfide bonds, while the Bowman-Birk inhibitor has a MW of 7,900 with seven disulfide bonds (Wolf, 1977). The large ratio of disulfide bonds to MW in the Bowman-Birk inhibitor stabilizes protein conformation and makes the Bowman-Birk inhibitor highly resistant to heat denaturation and inactivation. The Kunitz inhibitor inhibits trypsin, while the Bowman-Birk inhibitor inhibits both trypsin and chymotrypsin. The kinetics of TI inactivation when heating at high water activity were determined by Johnson et al. (1980) they estimated that 83-91% of the TI activity in soybeans is due to the Kunitz inhibitor. Recently, the Bowman-Birk inhibitor was attributed cancer-protecting qualities and also interest exists in using purified soy TI to treat AIDS patients (Kennedy, 1995, 1998 Kennedy Szuhaj, 1994). 

Snail epidermis contains at least six trypsin-kallikrein inhibitors with molecular weights ranging from 6431 to 6591 (70-72). The soybean contains two basic types of protease inhibitors, the Kunitz inhibitor of 21,500 daltons (73) and the Bowman-Birk inhibitor of 7975 daltons (74). The two are quite different proteins as shown in Figure 6. The Great Northern bean (Phaseolus vulgaris) has at least three trypsin isoinhibitors ranging in molecular weight from 8086 to 8884 (15). There are four and possibly six isoinhibitors of trypsin in lima bean (Phaseolus lunatus)(75). 

GM oilseed rape plants containing a gene encoding the protease inhibitor OCI, under the control of the CaMV 35S promoter, had measurable quantities of this transgene product in their leaves (0.2-0.4 percent of total soluble protein) but not in their pollen [16]. This finding was confirmed by Jouanin et al. [17], who also noted that Bowman-Birk soybean trypsin inhibitor (BBI) could not be detected in the nectar or pollen of GM oilseed rape plants which had measurable expression levels in leaves (gene also on the CaMV 35S promoter). 

A very interesting example may be the use of Bowman-Birk Inhibitor (BBI) from soybeans in the treatment of multiple sclerosis. Proteases generated during inflammation are involved in the induction of tissue damage during inflammatory demyelination in the central nervous system. Both in vitro and ex vivo, BBI inhibited myelin basic protein-specific proliferation of lymph node cells. BBI reduced the activity of matrix metalloproteinase-2 and -9 in spleen cell supernatants and was detected in the central nervous system of treated rats. BBI suppresses experimental autoimmune encephalomyelitis, it can be administered orally, and it is safe and relatively inexpensive. It may have a therapeutic role in patients with MS (Gran et al., 2006). 

---