Difference Between Parallel and Antiparallel Beta Pleated Sheets

The key difference between parallel and antiparallel beta pleated sheets is that in parallel beta pleated sheets, polypeptide strands run in the same direction, while in antiparallel beta pleated sheets, neighbouring strands run in opposite directions.

Beta pleated sheet or beta sheet is a common secondary structure of proteins. There are hydrogen bonds between beta strands forming a twisted pleated appearance. Polypeptide strand may run in the same direction or in the reverse direction. Based on that, there are two major types of beta sheets as parallel beta pleated sheets and antiparallel beta pleated sheets. In parallel beta pleated sheets, there are two polypeptide strands running in the same direction. In antiparallel beta pleated sheets, there are polypeptide strands running in the opposite directions.

CONTENTS

1. Overview and Key Difference
2. What are Parallel Beta Pleated Sheets
3. What are Antiparallel Beta Pleated Sheets
4. Side by Side Comparison – Parallel vs Antiparallel Beta Pleated Sheets in Tabular Form
5. Summary

What are Parallel Beta Pleated Sheets?

Parallel beta pleated sheets are the beta sheets that have two polypeptide strands running in the same direction. These secondary structures are less stable than antiparallel beta pleated sheets since the hydrogen bonds in parallel beta-sheet are not linear. There are 12 atoms in each hydrogen bonded ring in a parallel beta sheet.

In parallel beta sheets, all of the N-termini of polypeptide strands are oriented in the same direction. Parallel β sheets of less than five strands are rare since there are less stable hydrogen bonds between strands.

What are Antiparallel Beta Pleated Sheets?

Antiparallel beta pleated sheets are the second major type of beta sheets of proteins. In antiparallel beta sheets, the neighbouring two polypeptide strands run in the opposite direction. The number of atoms in each hydrogen bonded ring alternates between 14 and 10. Since hydrogen bonds in an antiparallel beta-sheet are linear, it is more stable than parallel beta sheets.

In antiparallel beta sheets, N-terminus of one strand is adjacent to the C-terminus of the next strand. This arrangement forms the strongest inter-strand stability. Antiparallel β-sheets are native proteins.

What are the Similarities Between Parallel and Antiparallel Beta Pleated Sheets?

• Parallel and antiparallel beta pleated sheets are two major types of beta sheets.
• In both types, polypeptide strands are held together by hydrogen bonding between the strands.
• Both forms are seen in native proteins.
• They are protein secondary structures.

What is the Difference Between Parallel and Antiparallel Beta Pleated Sheets?

Parallel beta pleated sheets have two polypeptide strands running in the same direction while antiparallel beta pleated sheets have two polypeptide strands running in the opposite directions. So, this is the key difference between parallel and antiparallel beta pleated sheets. Moreover, the hydrogen bonds in parallel beta sheets are less stable while the hydrogen bonds in antiparallel beta sheets are well oriented, strong and stable.

The below infographic lists the differences between parallel and antiparallel beta pleated sheets in tabular form.

Summary – Parallel vs Antiparallel Beta Pleated Sheets

Two polypeptide strands extend in the same direction in parallel beta sheets. In contrast, two polypeptide strands extend in the opposite direction in antiparallel beta pleated sheets. Moreover, the number of atoms in each hydrogen bonded ring in parallel beta sheets is 12 while it alternates between 14 and 10 in antiparallel beta sheets. When considering the stability of each type of beta sheet, antiparallel beta pleated sheets are more stable than parallel beta sheets. Thus, this is the summary of the difference between parallel and antiparallel beta pleated sheets.

Reference:

1. “Secondary Structure: β-Pleated Sheet.” Chemistry LibreTexts, Libretexts, 11 Aug. 2020, Available here.
2. “Antiparallel Beta-Sheet.” Antiparallel Beta-Sheet – an Overview | ScienceDirect Topics, Available here.

Image Courtesy:

1. “Beta sheet bonding parallel-color” By Fvasconcellos – Own work.Created by uploader upon request by Opabinia regalis. (Public Domain) via Commons Wikimedia
2. “Beta sheet bonding antiparallel-color” By Fvasconcellos – Own work.Created by uploader upon request by Opabinia regalis. (Public Domain) via Commons Wikimedia