Omega loop

Beginning and end of the loop come together

The shape appears similar to Greek Capital Omega

Compact Globular structure

No regular repeating pattern of hydrogen bonds

Side chains pack into the center of the loop

Omega loops have specific functions like

Omega loop from two proteins interact with each other to form dimers

Phosphate binding loop of nucleotide proteins

TLS Online TPP Program

#Id: 10227

#Unit 6. System Physiology – Plant

BR-deficient mutants exhibits extreme dwarfism, altered leaf morphology, abnormal vascular development, delayed flowering and senescence, and reduced male fertility.

TLS Online TPP Program

#Id: 10228

#Unit 6. System Physiology – Plant

brassinolide binds to brassinosteroid receptor kinase BRASSINOSTEROID-INSENSITIVE1 (BRI1) on the plasma membrane triggers a phosphorylation cascade that causes a repressor protein, BRASSINOSTEROID-INSENSITIVE2 (BIN2), to become inactivated.

TLS Online TPP Program

#Id: 10229

#Unit 6. System Physiology – Plant

TLS Online TPP Program

#Id: 10230

#Unit 6. System Physiology – Plant

Upon binding brassinolide, homodimers of BRI1 are activated and heterooligomerize with the RLK BRI1-ASSOCIATED RECEPTOR KINASE1 (BAK1)

TLS Online TPP Program

#Id: 10231

#Unit 6. System Physiology – Plant

BIN2 is a serine/threonine protein kinase that, in the absence of brassinolide, negatively regulates the closely related transcription factors BES1 and BZR1 by phosphorylation.

TLS Online TPP Program

#Id: 10232

#Unit 6. System Physiology – Plant

In the presence of brassinolide, the activated phosphatase BSU1 dephosphorylates BIN2 and promotes its degradation by the 26S proteasome system, thus blocking its activity. BES1 and BZR1

are then dephosphorylated by PROTEIN PHOSPHATASE2A

(PP2A), and the active forms of BES1 and BZR1 move into the nucleus where they regulate the expression of brassinolide response genes