Chemical Cleavage of Peptide Bonds
Roger L. Lundblad in Chemical Reagents for Protein Modification, 2020
A number of methods have been proposed for chemical cleavage at cysteine residues. One approach is based on the conversion of cysteine to dehydroalanine22-24 and subsequent hydrolysis with either acid or base to release pyruvic acid and involves the conversion of cysteine to the dialkyl sulfonic salt with methyl bromide or methyl iodide at pH 6.0 and subsequent β-elimination in dilute bicarbonate with mild heating.24 The use of 2,4-dinitrofluorobenzene for the modification of cysteine to form the S-dinitrophenyl derivatives at pH 5.6 has been reported.24 The β-elimination of these derivatives was accomplished with sodium methoxide in methanol. Cleavage of the dehydroalanine-containing peptide bond was accomplished by heating (100°C) in dilute acid (0.01 M HCl) for 1 h. This reaction mixture was then lyophilized, treated with a volume of 0.1 M NaOH equivalent to the original volume of acid and one fifth volume of 30% hydrogen peroxide and then heated at 37°C for 30 min. The reaction mixture was then neutralized with acetic acid and excess peroxide removed with catalase. Alternatively, cleavage can be accomplished with bromide or performic acid.
Defects in Tg Gene Expression and Tg Secretion
Geraldo Medeiros-Neto, John Bruton Stanbury in Inherited Disorders of the Thyroid System, 2019
Through a further action of the peroxidase, two DIT residues, both in peptide linkage within Tg, couple to form thyroxine (T4). This occurs by the formation of a diphenylether from the two DITs, leaving dehydroalanine at the site formerly occupied by the DIT donating the outer ring of T4. The other thyroid hormone, 3,5,3′-triiodothyronine (T3), is formed by coupling a molecule of MIT with one of DIT. Normally, about one third of the iodine of Tg will be in the thyroid hormones T4 and T3, the remainder being in the inactive precursors DIT and MIT. By the time hormone synthesis is completed, two chains of 330,000 Da will associate to form the mature 660,000-Da Tg molecule. The two associating chains are probably identical. Thyroglobulin is stored extracellularly in the lumen of the thyroid follicle, where it is virtually the sole occupant.
Proteins in Cosmetics
E. Desmond Goddard, James V. Gruber in Principles of Polymer Science and Technology in Cosmetics and Personal Care, 1999
Strongly alkaline treatments can cause degradation of some amino acids and formation of nonphysiological, potentially toxic molecules. Some of these transformations occur through dehydroalanine, a reactive molecule that is formed via β-elimination of from cysteine or via dehydration of serine. Dehydroalanine can condense with the ε-amino group of lysine, whereby the unnatural amino acid lysinoalanine is formed, or react with a second molecule of cysteine to give lanthionine (Fig. 4) .
An overview of lantibiotic biosynthetic machinery promiscuity and its impact on antimicrobial discovery
Published in Expert Opinion on Drug Discovery, 2020
Studies have shown that the biosynthetic genes involved in the modification of nisin, NisB dehydratase, NisT transporter and cyclase NisC, can be efficiently expressed in other organisms including Lactococcus lactis and Escherichia coli under the control of an inducible promotor. NisB and NisC act via the formation of a catalytically active complex, working in an alternating manner to introduce post-translational modifications into the core section of the pre-nisin. The NisB/NisC complex has been shown to only form in the presence of the pre-nisin substrate. The stoichiometry of the post-translational modification complex has been identified as 2:1:1 (NisB: NisC: pre-nisin) [40]. NisB dehydrates serine and threonine residues in the core peptide. During this process a glutamate is transferred from glutamyl RNAGLU to specific serine/threonine side chains within the core peptide introducing glutamylated intermediates [41]. These serine/threonine residues are then converted to dehydroalanine and dehydrobutyrine. NisC then catalyzes a Michael addition of a C-terminal cysteine residue with the dehydrated amino acids, forming thioether rings resulting in the formation of (methyl) lanthionine rings [42]. Studies have highlighted the ability of this system to modify and transport a broad range of subtrates not just lantibiotics, highlighting the broader potential application of this modification system [43–45].
An update on late-stage functionalization in today’s drug discovery
Published in Expert Opinion on Drug Discovery, 2023
Andrew P. Montgomery, Jack M. Joyce, Jonathan J. Danon, Michael Kassiou
Scamp et al. [77] utilized a Co(III)-catalyzed C(sp2)–H amidation of dehydroalanine (Dha) residues of the antibiotic thiostrepton (60) to produce novel derivatives with improved aqueous solubility. This method demonstrated complete selectivity for the Z-stereoisomer and was also site selective at the terminal Dha residue of thiostrepton (Dha1), with small amounts of diamidation generally observed (Figure 7C). Of the derivatives generated in this work, three (61–63) displayed an increased aqueous solubility ranging from a five- to nine-fold improvement (61: 16.2 ± 0.6 µg mL−1, 62: 28 ± 4 µg mL−1, 63: 19 ± 1 µg mL−1) compared to 60 (3.0 ± 0.2 µg mL−1). Derivatives 61–63 exhibited a reduced antimicrobial activity against a range of gram-positive organisms compared to 60, however they were able to retain potency comparable to vancomycin.
Current developments in lantibiotic discovery for treating Clostridium difficile infection
Published in Expert Opinion on Drug Discovery, 2019
Lantibiotics are ribosomally synthesized, post-translationally modified peptides containing unusual amino acids including lanthionine, and methyl-lanthionine. Modifications found in lantibiotics often include the formation of dehydroalanine and dehydrobutyrine residues caused by the dehydrations of serine and threonine residues, respectively. Lanthionine is formed when the dehydrated residues are cyclized with cysteines forming thioether bridges. Lantibiotics are subgrouped based on the biosynthetic enzymes involved in their production. Type I lantibiotics are modified by two enzymes, a dehydratase (LanB) and a cyclase (LanC) forming flexible elongated structures and are commonly positively charged and ampipathic. Type II lantibiotics are modified by a single enzyme (LanM) which functions as both a cyclase and dehydratase, these tend to be globular, carrying no net charge. For Type III and IV lantibiotics, dehydration is carried out by a central kinase domain and an N-terminal phosphoSer/phosphoThr lyase domain, however the C-terminal cyclization domain of the synthases between type III and IV differ with three metal binding residues that are conserved in type I, II, and IV lantibiotics being absent from type III [21–24].
Related Knowledge Centers
- Cysteine
- Enamine
- Hydrogen Sulfide
- Peptide
- Pyruvic Acid
- Serine
- Dehydroamino Acid
- Saturated & Unsaturated Compounds
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- Post-Translational Modification