Thermolysin
Encyclopedia
Thermolysin is a thermostable neutral metalloproteinase
enzyme
produced by the gram-positive
bacteria Bacillus thermoproteolyticus. It requires one zinc ion for enzyme activity and four calcium ions
for structural stability. Thermolysin specifically catalyzes the hydrolysis
of peptide bond
s containing hydrophobic amino acids. However thermolysin is also widely used for peptide bond formation through the reverse reaction of hydrolysis. Thermolysin is the most stable member of a family of metalloproteinases produced by various Bacillus
species. These enzymes are also termed 'neutral' proteinases or thermolysin -like proteinases (TLPs).
proteases thermolysin is first synthesised by the bacterium as a pre-proenzyme
. Thermolysin is synthesized as a pre-proenzyme consisting of a signal peptide
28 amino acids long, a pro-peptide 204 amino acids long and the mature enzyme itself 316 amino acids in length. The signal peptide acts as a signal for translocation
of pre-prothermolysin to the bacterial cytoplasmic membrane. In the periplasm pre-prothermolysin is then processed into prothermolysin by a signal peptidase
. The prosequence then acts as a molecular chaperone and leads to autocleavage of the peptide bond linking pro and mature sequences. The mature protein is then secreted into the extracellular medium.
s with a deep cleft running across the middle of the molecule separating the two domains. The secondary structure
of each domain is quite different, the N-terminal domain consists of mostly beta pleated sheet, while the C-terminal domain is mostly alpha helical in structure. These two domains are connected by a central alpha helix, spanning amino acids 137-151.
In contrast to many proteins that undergo conformational changes upon heating and denaturation
, thermolysin does not undergo any major conformational changes until at least 70 °C. The thermal stability of members of the TLP family is measured in terms of a T50 temperature. At this temperature incubation for 30 minutes reduces the enzymes activity by half. Thermolysin has a T50 value of 86.9 °C, making it the most thermo stable member of the TLP family. Studies on the contribution of calcium
to thermolysin stability have shown that upon thermal inactivation a single calcium ion is released from the molecule. Preventing this calcium from originally binding to the molecule by mutation
of its binding site, reduced thermolysin stability by 7 °C. However, while calcium binding makes a significant contribution to stabilising thermolysin, more crucial to stability is a small cluster of N-terminal domain amino acids located at the proteins surface. In particular a phenylalanine
(F) at amino acid position 63 and a proline
(P) at amino acid position 69 contribute significantly to thermolysin stability. Changing these amino acids to threonine
(T) and alanine
(A) respectively in a less stable thermolysin-like proteinase produced by Bacillus stearothermophillus (TLP-ste), results in individual reductions in stability of 7 °C (F63→T) and 6.3 °C (P69→A) and when combined a reduction in stability of 12.3 °C.
, less bitter-tasting byproduct is produced when the reaction is catalyzed by thermolysin.
Metalloproteinase
Metalloproteinases constitute a family of enzymes from the group of proteases, classified by the nature of the most prominent functional group in their active site. These are proteolytic enzymes whose catalytic mechanism involves a metal. Most metalloproteases are zinc-dependent, but some use...
enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
produced by the gram-positive
Gram-positive
Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain and appearing red or pink...
bacteria Bacillus thermoproteolyticus. It requires one zinc ion for enzyme activity and four calcium ions
Calcium in biology
Calcium plays a pivotal role in the physiology and biochemistry of organisms and the cell. It plays an important role in signal transduction pathways, where it acts as a second messenger, in neurotransmitter release from neurons, contraction of all muscle cell types, and fertilization...
for structural stability. Thermolysin specifically catalyzes the hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
of peptide bond
Peptide bond
This article is about the peptide link found within biological molecules, such as proteins. A similar article for synthetic molecules is being created...
s containing hydrophobic amino acids. However thermolysin is also widely used for peptide bond formation through the reverse reaction of hydrolysis. Thermolysin is the most stable member of a family of metalloproteinases produced by various Bacillus
Bacillus
Bacillus is a genus of Gram-positive, rod-shaped bacteria and a member of the division Firmicutes. Bacillus species can be obligate aerobes or facultative anaerobes, and test positive for the enzyme catalase. Ubiquitous in nature, Bacillus includes both free-living and pathogenic species...
species. These enzymes are also termed 'neutral' proteinases or thermolysin -like proteinases (TLPs).
Synthesis
Like all bacterial extracellularExtracellular
In cell biology, molecular biology and related fields, the word extracellular means "outside the cell". This space is usually taken to be outside the plasma membranes, and occupied by fluid...
proteases thermolysin is first synthesised by the bacterium as a pre-proenzyme
Protein precursor
A protein precursor, also called a pro-protein or pro-peptide, is an inactive protein that can be turned into an active form by posttranslational modification. The name of the precursor for a protein is often prefixed by pro...
. Thermolysin is synthesized as a pre-proenzyme consisting of a signal peptide
Signal peptide
A signal peptide is a short peptide chain that directs the transport of a protein.Signal peptides may also be called targeting signals, signal sequences, transit peptides, or localization signals....
28 amino acids long, a pro-peptide 204 amino acids long and the mature enzyme itself 316 amino acids in length. The signal peptide acts as a signal for translocation
Translocation
Translocation may refer to:* Chromosomal translocation, in genetics* Translocation in plants, transport of food or pesticides through phloem or xylem* Protein translocation or protein targeting, a process in protein biosynthesis...
of pre-prothermolysin to the bacterial cytoplasmic membrane. In the periplasm pre-prothermolysin is then processed into prothermolysin by a signal peptidase
Signal peptidase
Signal peptidases are enzymes that convert secretory and some membrane proteins to their mature form by cleaving off their N-terminal targeting signals....
. The prosequence then acts as a molecular chaperone and leads to autocleavage of the peptide bond linking pro and mature sequences. The mature protein is then secreted into the extracellular medium.
Structure
Thermolysin has a molecular weight of 34,600 Da. Its overall structure consists of two roughly spherical domainProtein domain
A protein domain is a part of protein sequence and structure that can evolve, function, and exist independently of the rest of the protein chain. Each domain forms a compact three-dimensional structure and often can be independently stable and folded. Many proteins consist of several structural...
s with a deep cleft running across the middle of the molecule separating the two domains. The secondary structure
Secondary structure
In biochemistry and structural biology, secondary structure is the general three-dimensional form of local segments of biopolymers such as proteins and nucleic acids...
of each domain is quite different, the N-terminal domain consists of mostly beta pleated sheet, while the C-terminal domain is mostly alpha helical in structure. These two domains are connected by a central alpha helix, spanning amino acids 137-151.
In contrast to many proteins that undergo conformational changes upon heating and denaturation
Denaturation (biochemistry)
Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent , or heat...
, thermolysin does not undergo any major conformational changes until at least 70 °C. The thermal stability of members of the TLP family is measured in terms of a T50 temperature. At this temperature incubation for 30 minutes reduces the enzymes activity by half. Thermolysin has a T50 value of 86.9 °C, making it the most thermo stable member of the TLP family. Studies on the contribution of calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
to thermolysin stability have shown that upon thermal inactivation a single calcium ion is released from the molecule. Preventing this calcium from originally binding to the molecule by mutation
Site-directed mutagenesis
Site-directed mutagenesis, also called site-specific mutagenesis or oligonucleotide-directed mutagenesis, is a molecular biology technique in which a mutation is created at a defined site in a DNA molecule. In general, this form of mutagenesis requires that the wild type gene sequence be known...
of its binding site, reduced thermolysin stability by 7 °C. However, while calcium binding makes a significant contribution to stabilising thermolysin, more crucial to stability is a small cluster of N-terminal domain amino acids located at the proteins surface. In particular a phenylalanine
Phenylalanine
Phenylalanine is an α-amino acid with the formula C6H5CH2CHCOOH. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. L-Phenylalanine is an electrically neutral amino acid, one of the twenty common amino acids used to biochemically form...
(F) at amino acid position 63 and a proline
Proline
Proline is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that the human body can synthesize it. It is unique among the 20 protein-forming amino acids in that the α-amino group is secondary...
(P) at amino acid position 69 contribute significantly to thermolysin stability. Changing these amino acids to threonine
Threonine
Threonine is an α-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar...
(T) and alanine
Alanine
Alanine is an α-amino acid with the chemical formula CH3CHCOOH. The L-isomer is one of the 20 amino acids encoded by the genetic code. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid...
(A) respectively in a less stable thermolysin-like proteinase produced by Bacillus stearothermophillus (TLP-ste), results in individual reductions in stability of 7 °C (F63→T) and 6.3 °C (P69→A) and when combined a reduction in stability of 12.3 °C.
Application
In the synthesis of aspartameAspartame
Aspartame is an artificial, non-saccharide sweetener used as a sugar substitute in some foods and beverages. In the European Union, it is codified as E951. Aspartame is a methyl ester of the aspartic acid/phenylalanine dipeptide. It was first sold under the brand name NutraSweet; since 2009 it...
, less bitter-tasting byproduct is produced when the reaction is catalyzed by thermolysin.
External links
- The MEROPSMeropsMerops may refer to:* Merops , a genus of bee-eaters.* MEROPS, an on-line database for peptidases.It may also refer to several figures from Greek mythology:* King of Ethiopia, husband of Clymene, who lay with Helios and bore Phaethon...
online database for peptidases and their inhibitors: M04.001