Purified chitinases and use thereof

Details Purified chitinases and use thereof Purified chitinases and use thereof

1992-07-27

2001-06-26

Prouty, Rebecca E. (Department: 1652)

Drug, bio-affecting and body treating compositions

Enzyme or coenzyme containing

Hydrolases

C435S209000, C435S069100, C514S012200

Reexamination Certificate

active

06251390

ABSTRACT:

TECHNICAL FIELD
This invention is directed to isolation of chitinases for biological control of chitin-containing fungi and insects.
BACKGROUND OF THE INVENTION
Application of broad-spectrum pesticides is the primary method used for controlling fungal and insect pests. Such application has resulted in significant environmental pollution and ecological disruption. Pesticide residues are found in food and groundwater and often eliminate beneficial organisms resulting in emergence of secondary pests. Furthermore, as the target pests become less susceptible to the pesticide, there can be a resurgence of the original pest, requiring application of excessive quantities of pesticides for control.
A number of strategies for biological or biorational control of fungal and insect pests have been envisioned. Among the more attractive strategies are those that target an attribute that is pest specific. One target that has been selected is the structural polymer chitin, which is present in insects and some fungi that attack plants, but is absent in higher plants and vertebrates. U.S. Pat. No. 4,751,081 follows this approach and is directed to novel chitinase-producing bacteria strains for use for inhibiting chitinase-sensitive plant pathogens (fungi and nematodes). The approach of U.S. Pat. No. 4,751,081 lacks flexibility.
SUMMARY OF THE INVENTION
An object of the invention herein is to provide purified chitinases which can be used per se to inhibit fungi and insects that contain chitin or can be used to provide novel chitinase-producing bacteria as in U.S. Pat. No. 4,751,081 or can be used to isolate genes coding for them which can be inserted into a genome of a plant needing protection from a chitin-containing pest.
The chitinases that are the subject of the instant invention are isolated from
Trichoderma harzianum
strain P1. This strain was deposited with the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Md. 20852 on May 20, 1991, under the terms of the Budapest Treaty, and has been assigned accession number ATCC 74058.
The chitinases herein inhibit chitin-containing fungi and insects.
One chitinase herein is an essentially pure protein and has endochitinase activity and has a molecular weight of 36 kDa (as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis after the protein was prepared under reducing conditions, on direct comparison to migration of a 36 kDa protein) and an isoelectric point of 5.3±0.2 as determined based on its elution profile from a chromatofocusing column. It has a molecular weight of 40 kDa (as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis after the protein was prepared under reducing conditions, from a regression based on the log of the molecular weight of standard proteins) and an isoelectric point of 3.9 as determined by isoelectric focusing electrophoresis from a regression of distance versus isoelectric point of standard proteins. It has an optimum activity at about pH 4 with a gradual decline to about pH 7. This chitinase is sometimes described hereinafter as the endochitinase herein.
Another chitinase herein has exochitinase activity and has a molecular weight of 36 kDa (as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis after the protein was prepared under reducing conditions, on direct comparison to migration of 36 kDa protein) and an isoelectric point of 4.4±0.2 as determined based on its elution profile from a chromatofocusing column. It has a molecular weight of 40 kDa (as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis after the protein was prepared under reducing conditions, from a regression based on the log of the molecular weight of standard proteins) and an isoelectric point of 3.9 as determined by isoelectric focusing electrophoresis from a regression of distance versus isoelectric point of standard proteins. It has chitobiase activity, as indicated by its substrate specificity. It has an optimum activity between pH 4 and pH 7. This chitinase is purified to greater than a 75-fold increase in specific activity compared to its activity in a culture filtrate of
Trichoderma harzianum
strain P1 having accession No. ATCC 74058. This chitinase may be obtained as an essentially pure protein or in purified condition may be present with a minor amount, e.g., up to 40% by weight (total chitobiase basis), of a chitobiase having a molecular weight of 36 kDa (as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis after the protein was prepared under reducing condition, from regression based on the log of the molecular weight of standard proteins) and an isoelectric point of 3.9 as determined by isoelectric focusing electrophoresis from a regression of distance versus isoelectric point of standard proteins. This chitinase in the form of an essentially pure protein may be described hereinafter as the chitobiase herein.
These chitinases are sometimes referred to collectively hereinafter as the “purified chitinases herein” or as chitinases “of the invention herein”.
Where the molecular weight was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis after the protein was prepared under reducing condition, from regression based on the log of the molecular weight of standard proteins, the proteins were seven standard proteins obtained from Sigma Chemical Co., having molecular weights ranging from 14.2 to 66 kDa, and molecular weights were estimated from a regression equation of the log of molecular weight of the standard proteins versus distance migrated; the seven standard proteins and their molecular weights in kDa are respectively &agr;-lactalbumin, 14.2; soybean trypsin inhibitor, 20.1; trypsinogen, phenylmethylsulfonyl fluoride treated, 24; carbonic anhydrase, 29; glyceraldehyde-3-phosphate, 36; egg albumin, 45; and bovine albumin, 66. When the isoelectric point was determined by isoelectric focusing electrophoresis from a regression of distance versus isoelectric point of standard proteins, comparison was to 12 standard proteins obtained from Pharmacia LKB Biotechnology having isoelectric points ranging from pH 3.5 to pH 9.3; the standard proteins and their isoelectric points are respectively amyloglucosidase, 3.5; methyl red dye, 3.75; soybean trypsin inhibitor, 4.55; &bgr;-lactoglobulin, 5.2; bovine carbonic anhydrase B, 5.85; human carbonic anhydrase B, 6.55; horse myoglobin cynocytic band, 6.85; horse myoglobin basic band, 7.35; lentil lectin acidic band, 8.15; lentil lectin middle band, 8.45; lentil lectin basic band, 8.65; and trypsinogen, 9.3. In both cases a linear regression was employed and r
2
values ranged from 0.94 to 0.99. For determination of pH optima, 50 mM citric acid and 50 mM of either K
2
HPO
4
(endochitinase) or K
3
PO
4
(chitobiase) were prepared and these two solutions were mixed in various ratios to give various pH values and assays were run in triplicate for each pH value and nitrophenyl-&bgr;-D-N,N′-diacetylchitobioside and nitrophenyl-&bgr;-D-N,N′,N″-triacetylchitotriose were used as substrates for chitobiase and endochitinase respectively.
A further embodiment of the invention herein involves a biologically pure (i.e., free of contaminating protein) composition containing endochitinase (enzyme that cleaves chitin randomly) and chitobiase (enzyme that cleaves dimeric units from chitin), preferably the endochitinase herein and the chitobiase herein, in a weight ratio ranging from 3:1 to 1:1.2.
The term “essentially pure” is used herein to mean the presence of a single protein band on a sodium dodecyl sulfate polyacrylamide gel submitted to electrophoresis under reducing conditions and stained with silver stain. The term “in purified condition” means “essentially pure” with exception as stated.
The term “inhibit” is used herein to mean reduce the growth and/or development of fungi or insects compared to where inhibiting agent is not present.
The term “endochitinase activity” is used herein to mean ability to cleave chitin randomly. Such activit

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