Identification of Protein Motifs using PROSITE – B.Sc. Bioinformatics Practical

 

Identification of Protein Motifs using PROSITE – B.Sc. Bioinformatics Practical

Aim of the Experiment

To identify conserved motifs and functional domains in a protein sequence using the PROSITE database.

Principle

PROSITE is a database of protein families and domains that uses patterns and profiles to detect conserved motifs in protein sequences.

• Motifs are short conserved regions associated with specific functions
• PROSITE uses:
  • Patterns (regular expressions)
  • Profiles (position-specific scoring matrices)
• It helps predict protein function based on sequence similarity

The tool is accessed via ExPASy using the PROSITE Scan tool.

Requirements

• Computer with internet access
• Protein sequence (FASTA format)
• Access to:
  • ExPASy
  • PROSITE (ScanProsite tool)

Step-by-Step Procedure

Step 1: Retrieve Protein Sequence

• Visit NCBI
• Search for a protein (e.g., insulin, hemoglobin)
• Download sequence in FASTA format

Step 2: Open PROSITE Tool

• Go to ExPASy
• Navigate to ScanProsite tool

Step 3: Input Protein Sequence

• Paste the FASTA sequence into the input box
• Ensure sequence is in correct format

Step 4: Set Parameters (Optional)

• Select:
  • Scan for patterns and profiles
  • Include high sensitivity if required

Step 5: Run the Analysis

• Click “Scan”
• Wait for processing

Step 6: View Results

• Output displays:
  • Detected motifs
  • Position in sequence
  • PROSITE ID
  • Functional annotation

Typical Protein Motif Output

6

Step 7: Interpret Motifs

• Identify:
  • Functional domains (e.g., kinase domain)
  • Active sites
  • Binding regions

Step 8: Record Observations

• Note:
  • Protein name
  • Sequence length
  • Motif name
  • Position of motif
  • Function

Result

Motif Name	PROSITE ID	Position	Function
Protein kinase domain	PS50011	45–300	Catalytic activity
ATP binding site	PS00107	10–20	Energy binding

 Precautions

• Use correct protein sequence
• Ensure FASTA format is proper
• Avoid incomplete sequences
• Cross-check motif function

Applications

• Functional prediction of proteins
• Domain identification
• Drug target analysis
• Comparative genomics
• Protein classification

Viva Voce Questions (with Answers)

1. What is PROSITE?
   A database for protein motifs and domains.
2. What is a motif?
   A conserved sequence region with functional significance.
3. What is ScanProsite?
   A tool to identify motifs in protein sequences.
4. What are patterns in PROSITE?
   Regular expressions describing motifs.
5. What are profiles?
   Position-specific scoring matrices.
6. Which portal provides PROSITE tools?
   ExPASy
7. What is FASTA format?
   Standard sequence representation format.
8. Why are motifs important?
   They indicate protein function.