Cis peptidebond The cis and trans peptide bonds refer to the two possible spatial arrangements around the peptide bond, a crucial linkage in proteins and peptides. While the vast majority of peptide bonds in naturally occurring proteins adopt the trans configuration, the cis conformation, though less common, plays significant roles in protein structure and function, particularly where they involve specific amino acids like proline. Understanding these conformations is foundational to comprehending protein folding, stability, and the mechanisms of various biological processes.
A peptide bond forms between the carboxyl group of one amino acid and the amino group of another, releasing a water molecule. This bond has a partial double-bond character due to resonance, which restricts rotation around the C-N bond. This restricted rotation leads to the existence of two geometric isomers: cis and trans.
In the trans configuration, the alpha carbons of the two adjacent amino acid residues are on opposite sides of the peptide bond. This arrangement is generally favored due to lower steric hindrance between the side chains of the amino acidsPeptide bonds can have two conformations. The torsion angle ω (Cαi-1-Ci-1-Ni-Cαi) can bearound 0°, cis, or around 180°, trans. The peptides in the protein .... In fact, for most peptide bonds, the trans configuration is preferred by a ratio of approximately 1000:1 compared to the cis configuration.
In the cis configuration, the alpha carbons are on the same side of the peptide bond. This conformation is energetically less favorable due to potential clashes between the R-groups of adjacent amino acids作者：S Das·2014·被引用次数：11—Peptidesamenable tocis-transisomerization have been considered to be good targets for therapeutic interventions [12].Cis-transisomerization .... However, the cis conformation is not entirely absent and can occur, especially under specific circumstances.Video: Peptide Bonds
A notable exception to the general preference for the trans configuration involves the amino acid proline. When a peptide bond is formed between an amino acid and proline (an X-Pro bond), the cis conformation becomes significantly more populatedAmino Acid Cis Peptide Bond Formation - Let's Talk Academy. This is because proline's unique cyclic structure, where its side chain is attached to its own amino group, reduces the steric repulsion in the cis conformation compared to other amino acids作者：D Pal·1999·被引用次数：404—Due to the energy barrier,cis-trans isomerization of peptide bondis a rather slow process at room temperature and has been shown to play an important role in .... Consequently, proline-containing peptide bonds are more prone to adopting the cis configuration, and this isomerization is crucial for certain protein folding events and the formation of specific protein structures like turns.Peptide bonds revisited
Despite being less common, cis peptide bonds are not merely anomalies; they are integral to the structural and functional dynamics of many proteins.
* Protein Folding and Dynamics: The cis-trans isomerization of peptide bonds, particularly those involving proline, is a rate-limiting step in the folding of many proteins. This process, though slow at room temperature, is essential for achieving the correct three-dimensional structure. Some enzymes called peptidyl-prolyl isomerases (PPIases) catalyze this isomerization, accelerating protein folding.
* Structural Features: Cis peptide bonds can introduce kinks or turns in polypeptide chains.Different cis/trans configurations of the peptide bond. They are often found in specific structural motifs like beta-turns, which are important for protein secondary structure and overall protein architecture. The presence of a cis peptide bond can influence the local conformation and stability of the protein.
* Biological Roles: The occurrence of cis peptide bonds has been linked to protein function, including enzyme activity and signal transduction作者：J Chen·2012·被引用次数：19—Thecis peptide bondis a characteristic feature of turns in protein structures and can play the role of a hinge in protein folding.. In some cases, the cis conformation may be required for a protein to adopt its active form or to interact with other molecules. Research suggests that changes between cis and trans conformations can be associated with the evolution of new protein functions.
Several factors influence whether a peptide bond exists in the cis or trans conformation:
* Amino Acid Identity: As mentioned, proline is a key determinant. Other amino acids with bulky side chains can also increase the likelihood of cis peptide bond formation due to steric interactionsOccurrence and role of cis peptide bonds in protein structures.
* Surrounding Environment: The local environment within a protein, including interactions with other amino acid residues and the solvent, can affect the energetic favorability of cis versus trans conformations.
* Temperature and pH: These external factors can influence the rate of cis-trans isomerization作者：KP Exarchos·2009·被引用次数：36—Apeptide bondwas considered to be incisconformation if the ω angle was between −30° and +30°, whereas bonds with angles 180°(±30°) were assumed to be in ....
* Catalysis: PPIases play a critical role in facilitating the cis-trans isomerization of peptide bonds, especially in vivo.
The primary distinction between cis and trans peptide bonds lies in the relative positions of the alpha carbons of the adjacent amino acid residues with respect to the peptide bond plane. This geometric difference leads to variations in bond angles, distances between atoms, and overall protein backbone conformation. While X-ray crystallography and NMR spectroscopy are key techniques for determining these conformations in proteins, computational methods are also employed to predict the likelihood of cis or trans configurations for specific peptide bonds.
In summary, while the trans configuration is overwhelmingly dominant in peptide bonds due to energetic preferences, the cis peptide bond is a critical element in protein structure and functionOn the Cis to Trans Isomerization of Prolyl–Peptide Bonds .... Its occurrence, particularly adjacent to proline residues, influences protein folding kinetics, introduces specific structural features, and contributes to the diverse biological roles of peptides and proteins.
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