Protein Structure Prediction Overview
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Questions and Answers

What percentage of human protein-protein interactions have either X-ray or NMR structures?

  • 8% (correct)
  • 20%
  • 60%
  • 40%
  • Deep learning methods have shown that heterodimers generally have weaker correlated mutations compared to homocomplexes.

    False (B)

    What is the main improvement noted from CASP12 to CASP15?

    Substantial improvement in protein-protein docking.

    The technique used to combine sequences and predict structures using AI is called ________.

    <p>AlphaFold</p> Signup and view all the answers

    Match the terms with their correct descriptions:

    <p>AlphaFold = AI model for protein structure prediction CASP = Community-wide experiment on protein structure prediction Deep Learning = Method utilizing neural networks to improve predictions Correlated Mutations = Signals indicating functional interactions in protein complexes</p> Signup and view all the answers

    What is the primary function of the diffusions model in protein structure prediction?

    <p>To learn to reverse the noise addition process (D)</p> Signup and view all the answers

    An important step in machine learning for protein docking is ensuring that homologous sequences are included in both training and validation datasets.

    <p>False (B)</p> Signup and view all the answers

    What do proteins need to exhibit for successful rigid body docking?

    <p>Shape complementarity and electrostatic complementarity</p> Signup and view all the answers

    The primary aim of protein docking is to predict the structure of a complex starting with the __________ components.

    <p>unbound</p> Signup and view all the answers

    What is the significance of the PDB in relation to protein docking?

    <p>It has numerous known hetero-dimers. (D)</p> Signup and view all the answers

    In ab initio docking, a template-based approach is preferred due to the limited number of known complexes.

    <p>False (B)</p> Signup and view all the answers

    Match the following types of protein docking with their characteristics:

    <p>Ab initio docking = No template-based approach with rigid body assumptions Homology modeling = Based on comparison to known structures Rigid body docking = Evaluates shape and electrostatic complementarity Template-based docking = Utilizes existing structures for predictions</p> Signup and view all the answers

    What does 'global search' refer to in the context of protein docking?

    <p>Finding a good overlap of protein surfaces</p> Signup and view all the answers

    What metric measures the local agreement between two protein structures?

    <p>Predicted Distance Difference Test (pLDDT) (B)</p> Signup and view all the answers

    PLDDT values below 50 indicate a high degree of confidence in predictions.

    <p>False (B)</p> Signup and view all the answers

    What does pLDDT stand for?

    <p>predicted local distance difference test</p> Signup and view all the answers

    The __________ metric assesses how well the predicted distances between residues are aligned.

    <p>Predicted Alignment Error (PAE)</p> Signup and view all the answers

    Which stage of AlphaFold2 involves calculating residue-residue contacts?

    <p>Evoformer (C)</p> Signup and view all the answers

    Match the following accuracy metrics with their descriptions:

    <p>pLDDT &gt; 90 = High accuracy pLDDT 70-80 = Generally good backbone prediction pLDDT 50-70 = Low confidence pLDDT &lt; 50 = Often disordered with ribbon-like appearance</p> Signup and view all the answers

    AlphaFold2 predicts high confidence for all residues in the human proteome.

    <p>False (B)</p> Signup and view all the answers

    What algorithm is primarily used for refining structures in AlphaFold2?

    <p>Amber</p> Signup and view all the answers

    Flashcards

    Correlated Mutations

    A method for predicting protein-protein interactions by analyzing evolutionary relationships between amino acids in different proteins.

    AlphaFold2

    A powerful tool for predicting protein structures, including protein complexes, using deep learning.

    AlphaFold Multimer

    A version of AlphaFold2 designed to predict the structures of protein complexes.

    Residue-Residue Interaction Scoring

    A technique for predicting protein-protein interactions using scoring functions that evaluate the interactions between individual amino acids.

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    Template Docking

    A method for predicting protein-protein interactions by analyzing the evolutionary relationships between proteins.

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    Diffusion in protein structure prediction

    A process that progressively adds noise to a set of 3D coordinates, disrupting their structure and eventually leading to a random distribution.

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    Diffusion model in protein structure prediction

    A deep neural network that learns to reverse the diffusion process, predicting the original 3D coordinates of a protein from a noisy representation.

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    Forward diffusion in protein structure prediction

    The initial stage of diffusion that adds noise to the protein's 3D coordinates, disrupting its structure.

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    Reverse diffusion in protein structure prediction

    The stage of diffusion where the model learns to predict the original structure from the noisy representation.

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    Protein docking

    A technique used in protein structure prediction involves predicting the structure of a protein complex, starting with its unbound components.

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    Ab initio docking

    The first approach to protein docking, which uses a trial-and-error method to search for the best fitting arrangement between two unbound proteins

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    Rigid body docking

    A crucial aspect of protein docking where the proteins are treated as rigid bodies, allowing for a simpler and more efficient way to determine their interaction.

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    Global search in protein docking

    A step in ab initio docking where the algorithm looks for a good overlap of the surfaces of two proteins, indicating potential for interaction.

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    What is a distogram in AlphaFold2?

    AlphaFold2 uses a deep learning approach to predict the probable distance between residues, which can be visualized in a distogram.

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    How does AlphaFold2's two-track learning work?

    AlphaFold2 employs a two-track learning process: Evoformer and Structure networks. Evoformer focuses on calculating residue-residue contacts at different distances, while the Structure network predicts residue positions independently and optimizes for structural accuracy.

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    What are the inputs for AlphaFold2?

    AlphaFold2 uses a multiple sequence alignment of the query sequence and known PDB structures as input, which serves as templates for structural insights.

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    What is pLDDT in AlphaFold2?

    pLDDT (predicted local distance difference test) assesses the accuracy of individual residues in a protein structure predicted by AlphaFold2. A higher pLDDT score indicates more confidence in the prediction.

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    What is PAE in AlphaFold2?

    PAE (predicted alignment error) measures the accuracy of predicted distances between residues in a protein structure. It is used to assess the confidence in domain packing, with lower values indicating more reliable predictions.

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    How does AlphaFold2 refine its predictions?

    AlphaFold2 uses Amber molecular dynamics to refine the predicted structure, improving local stereochemistry while not necessarily enhancing overall RMSD.

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    What are some limitations of AlphaFold2?

    Despite achieving high accuracy for 98.5% of human proteins, AlphaFold2 predictions are only highly confident (pLDDT > 70) for about 65% of the human proteome.

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    What is a potential caveat of low PAE scores?

    While a low PAE generally indicates reliable domain packing, there are instances where very low PAE regions in AlphaFold2 predictions could be incorrectly positioned, leading to biologically unrealistic structures.

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    Study Notes

    Protein Structure Prediction

    • Over 250 million protein sequences exist, but fewer than 110,000 structures are known. This represents a significant gap.
    • The hypothesis is that a protein's sequence in an environment dictates its structure. Aiming to predict structure from a protein's sequence.

    Reasons for Predicting Protein Structure

    • To understand the relationship between sequence and structure.
    • To predict protein function based on structure.
    • To guide rational drug design.
    • To aid in rational mutagenesis studies.
    • To assist in deriving structures from experimental data.

    Quantifying Predicted Model Accuracy

    • RMSD (Root Mean Squared Deviation): A useful measure for similar structures. Typically, around 70 out of 90 superposed residues have an RMSD of 2.6 Å between a predicted and an experimental (x-ray) structure.
    • RMSD Limitations: Evaluating RMSD becomes less accurate as the differences between predicted and real structures increase. Comparing RMSD values across proteins with different lengths is challenging.
    • TM (Template Modelling): Removes arbitrary choices, such as maximum difference between equivalent residues. TM scores range from 0 to 1 and consider all residue equivalences. It is scaled by the length of the protein. A TM score > 0.5 indicates a good overall protein fold, while a value > 0.75 suggests a well-predicted structure.

    Template-Based Modelling – Phyre2.2

    • Query Sequence: The process starts with a query protein sequence.
    • Database Search: The protein sequence is compared against a large database of known structures.
    • Extracting Information: Secondary structure and sequence are extracted from known structures.
    • Multiple Sequence Alignment (MSA): The sequence is run through PSI-BLAST to generate an MSA.
    • Predicting Secondary Structure: The MSA is input into PSI-Pred to predict secondary structure.
    • Hidden Markov Models (HMMs): Models are created and matched to the query sequence. This allows for identification of homologous structures and remote relationships in the database.
    • Alignment and Refinement: An alignment between the query sequence and a known structure is created, and adjustments are made, considering residue insertions and deletions.
    • Loop Modelling: Used to model insertions and deletions within the sequence based on the alignment and predicted structure.

    Energy Minimisation

    • The method aims to compute a protein's energy potential, adjust its bond geometry, and work towards the energy minimum to achieve a thermodynamically stable conformation.
    • A challenge is getting trapped in local minima.

    Secondary Structure Prediction

    • This effort focuses on identifying local structural elements in a protein (α-helices, β-sheets, coils, and turns).
    • Often, multiple aligned protein sequences are used to provide supplementary information.

    Tertiary Structure Prediction

    • Predicts the 3D arrangement of all amino acids in a protein.
    • Template-based, template-free, and hybrid approaches (deep learning with templates) are employed.

    Hybrid Prediction – AlphaFold2

    • MSA (Multiple Sequence Alignment): Creates an alignment of sequences similar to the target sequence.
    • Evoformer and Structure Networks: Calculating residue-residue contacts using deep learning networks.
    • Refined Structure: Finally, a refined protein structure is generated.
    • PLDDT (Predicted Local Distance Difference Test): Measures the accuracy of predicted structures. High values (> 90) indicate high accuracy.

    Fragment-Based Prediction

    • Builds tertiary structure from smaller fragments from a database, assuming that local sequence determines local structure.
    • Fragments are constructed based on sequence alignment to known 3D arrangements of smaller structures.
    • Reasonable predictions, but sometimes incomplete or require integration with template-based strategies.
    • Uses evolutionary relationships (correlated mutations) to anticipate contacts between amino acid residues.

    Language Models

    • They predict connections between amino acids by considering known mutations in protein sequences from similar protein families for improved accuracy.
    • Predicting residue-residue contacts to build a 3D structure using deep learning.

    Protein Docking

    • Predicting the structure of a complex of two or more protein molecules starting from their unbound structures. Important for understanding protein interactions.
    • Approaches include ab initio methods (no template) and template-based methods.
    • The primary methods are rigid body docking followed by refining the positions of side chains, aiming to predict the lowest energy conformation.

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    Explore the critical gap between known protein sequences and structures and the importance of predicting protein structure from sequence. This quiz covers the relationship between sequence and structure, methods for model accuracy quantification, and implications for drug design and mutagenesis studies.

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