Brassinosteroids are a group of about 30 naturally occurring, growth-promoting compounds found in plants. Although they are known to promote growth, there is a great deal about them that remains unknown. Understanding the how, where, and why of their functioning could lead to important advances in plant science and agriculture. The first brassinosteroid to be isolated was brassinolide. Like other brassinosteroids, brassinolide can be viewed as though it were a key that fits perfectly into only one lock. And that lock is located in a doorknob, somewhere. Locating that doorknob, as well as figuring out how exactly the key fits and how the lock works could open a door, behind which a treasure of new knowledge and beneficial uses can be found.
 


A large class of turpenoids (an extensive group of natural products whose structures are composed of isoprene units [see below]) including many biologically important compounds.  More than 20,000 steroids are known, of which about 2% have some medical significance.  Structurally, steroids are derivatives of the hydrocarbon cyclopentanoperhydrophenanthrene (see below).  The nomenclature of the tetracyclic (four member) ring structure (often referred to as the steroid ‘nucleus’) and the numbering of its carbon atoms are shown. *

General Steroids


A class of growth promoting steroids widely distributed in higher plants, and also found in lower plants, including cyanobacteria.  About 30 naturally occurring brassinosteroids are known, and a number of analogues have been synthesized.  It has been shown that the structural features required for their unique biological activity are: (i) a cis-vicinal glycol moiety at C2/C3, (ii) a trans junction between rings A and B, (iii) an oxygen function at C6 in the form of a ketone, or a lactone, (iv) a vicinal glycol moiety at C22/C23.  Although brassinosteroids have been shown to promote growth... their physiological role is not clear. *

Notes:
Vicinal -- things attached to two neighboring carbons.
cis -- attached groups on the same side of the plane of the rings or a specific bond.
trans -- attached groups on the opposite sides of the plane of the rings or a specific bond.
Moiety -- one of two (or more) parts into which something is divided.
All of the rings are attached to each other in a trans-conformation, which tends to make the rings all lie in the same general plane.


BCPS (Biotin-Tagged Photoaffinity Castasterone)


A type of vitamin.  A dietary requirement is implied in the word vitamin.  Biotin is a coenzyme (catalyst) in various carboxylation reactions.  It is the “skin vitamin”.

Photoaffinity -- a chemical species has photoaffinity when electromagnetic radiation can make it chemically reactive so that it will covalently bond to another molecule.

Photoaffinity Labeling  -- a technique in which a photochemically reactive molecular entity, specifically associated with a biomolecule, is photoexcited in order to covalently
attach a label to the biomolecule, usually via intermediates.
    1996, 68, 2259  IUPAC Compendium of Chemical Terminology 2nd Edition (1997)


Brassinosteroids bind directly to the 94 amino acids comprising ID-LRR22 in the extracellular domain of BRI1. 

ID – Island Domain – a segment that is substantially isolated from the rest of the protein.

Domain – a distinct structural unit of a protein – may fold independently and have unique function relative to the other part(s) (domains) of the protein.

LRR – Leucine Rich Repeats – “Leucine-rich repeats (LRRs) are 20-29-residue sequence motifs present in tandem arrays (in) a number of proteins with diverse functions… The primary function of these motifs appears to be to provide a versatile structural framework for the formation of protein-protein interactions.”   http://pfam.wustl.edu/cgi-bin/getdesc?name=LRR_1

A Leucine Compound

Note that X and Y may be more Leu in a LRR.  Leucine is nonpolar and hydrophobic.


* Concise Encyclopedia: Biochemistry and Molecular Biology, 3rd Ed.,
Walter de Gruyter, Published 1997

 
 
 

Created by:
Jenna Krohn, Steven Bluder, Ryan Delgado, Jonathan Halevy, Mike McGuire, Charles Peterson, Jessica Schmidt, Tate Tolson,
Tiffany Vo, Laurie Zarnow
 
 

Created For:
Dr. Frans Tax @
The Original Paper

 
Home  |  Summary  |  Methods  |  Glossary