LRRK2 Quaternary Structure Influences Enzymatic Activity

My poster at SFN:

Poster Session 342, Parkinson's Disease: Cells and Mechanisms II, which will be held on Monday, November 17, 2008 in the Washington Convention Center: Hall A-C. The session will begin at 8:00am

Abstract Title: LRRK2 quaternary structure influences enzymatic activity
Presentation Number: 342.6
Presentation Time: 9:00am - 10:00am
Poster Board Number: Q1

Abstract

The leucine-rich repeat kinase 2 (LRRK2) protein, as part of a ‘druggable’ class of proteins, represents a viable target for therapeutic modulation in Parkinson’s disease through the identification of small molecule kinase inhibitors. Mutations in the LRRK2 gene cause late-onset Parkinson’s disease clinically and neurochemically indistinguishable from typical idiopathic disease. In cells, we find that LRRK2 protein forms complex higher order conformations. Herein, we investigate the relationship between the oligomeric forms of the protein in the disease-associated mutants as compared to the wild-type protein. We genetically and pharmacologically dissect the effect of higher-order LRRK2 structures on kinase activity and neurotoxicity. Our results show that quaternary structure confirmations critically influence LRRK2 activity in cells.

Phosphorylation of LRRK2: Functional characterization

The poster in SFN on the above topic by G. Ito et al talks about the N-terminal Serine residues (Ser 910 and Ser 973). The authors claimed in the abstract that mutating these residues did not alter the Kinase of GTPase activity of the protein. What it appears to me that these residues might not be the ones which governs the Kinase or GTPase activity in PD-related patients. I will look forward for more results in the meeting.

LRRK2 in SFN

SFN (The Society for Neuroscience) Annual meeting is coming up in mid-November, at Washington DC, USA.
A lot of abstracts have been submitted for both poster and talk sessions. There are a couple of abstracts dealing with various aspects of LRRK2. I will subsequently discuss these abstracts and my views on them from now on: leading upto the meeting: which should eventually generate a healthy discussion when we meet all the presenters at the meeting.

LRRK2 Therapeutics

The other significant gene which acts as a major player in the autosomal dominant PD is the LRRK2. It was first identified in a Japanese population in 2002 and first cloned in 2004.
The great significance of this gene is that it has both kinase activity and GTPase activity encoded within the same molecule. Literature report also suggests that the Kinase activity is governed by the GTPase activity, however, the GTPase activity is normal even if the kinase activity is ablated.
Targeting for small molecule inhibitors for ablation of kinase activity will be a possible therapeutic target for the disease.

Therapeutic targets for PD (Contd..)

As discussed before, targeting alpha-synuclein for prevention of neurodegeneration and vying for neurorestoration would be a good therapeutic target. alpha-synulein aggregation has been one of the most widely cited cause leading to Lew Bodies and finally to Dopamineric cell death. Now: what causes the alpha-synuclein molecule to aggregate ? What is the mechanism of the aggregation ?
Being the most abundant protein comprising the proteinacious aggregates that define PD on pathologic level, intense efforts revolve around understanding alpha-synuclein accumulation and aggregation. alpha-synuclein may assume oligomeric species through unknown mechanisms, and higher-order alpha-synuclein structures usually correlate with toxicity in cells. What specific conformational entities are directly responsible for protection, toxicity and/or aggregation remain elusive. Factors known to modify alpha-synuclein aggregation and/or oligomerization include mutations in the primary amino acid sequence (e.g., PD-associated mutations: A30P, E46K, A53T), C-terminal truncations, interactions with metal ions, interactions with Aβ peptide, interactions with chaperone proteins such as Hsp40, Hsp70, interactions with apolipoprotein E, as well as neurotoxins, pesticides and herbicides, organic solvents, tyrosine nitration, phosphorylation, methionine oxidation, monoubiquitination, interaction with polyanions & polycations, oxidative dimers, histones, transglutaminase, and other protein-protein interactions, as well as other processes including mitochondrial dysfunction, oxidative stress, neuroinflammation, l-DOPA treatment and DA metabolism etc.

As a potential therapeutic target of action, the accumulation of alpha-synuclein into insoluble protein inclusions seems to be an important event in pathogenesis, yet a strong case can be made for therapeutically promoting inclusion formation in disease to protect cells from more soluble toxic species, as well as therapeutically dissolving inclusions to relieve the cells of a deleterious organelle that disrupts normal function. This dichotomy hinders alpha-synuclein as a viable target for therapeutics.

Therapeutic targets for PD

As LRRK2 and alpha-synuclien are the two most important genes involved in the pathological manifestation of PD, these are the obvious two candidates which can be targeted for therapeutic purposes. The main approach would be to stop or slow the progression of the disease: and the best therapy possible would be complete reversal.

What are the aliases for LRRK2

LRRK2 is known by a host of other different names: both the gene of the gene product. The commonly used aliases for LRRK2 are:

* DKFZp434H2111 * Dardarin
* FLJ45829 * LRRK2_HUMAN
* PARK8 * RIPK7
* ROCO2

Where is LRRk2 located ?

If you have ever wondered where LRRK2 is found in the human chromosome:

Cytogenetic Location: 12q12

Molecular Location on chromosome 12: base pairs 38,905,085 to 39,051,869

In details:

The LRRK2 gene is located on the long (q) arm of chromosome 12 at position 12.

More precisely, the LRRK2 gene is located from base pair 38,905,085 to base pair 39,051,869 on chromosome 12.

What are your chances of inheriting PD

If any member of your family has a history of PD, it is highly probable that you might be predisposed to the disease. The gene which has created a buzz in the scientific community for its role in PD is LRRK2. It is a relatively new gene and lots of scientific research is being carried out now and information is pouring in at a constant pace.
The mutation which has been prominent is the G2019S mutation on the LRRK2 gene found in chromosome 12. The single-letter change in the DNA code dramatically increases a person’s odds of developing Parkinson’s from one or two in a hundred to as much as eight in 10. One recent study found that a person who inherits the mutation has a 28% chance of developing Parkinson’s by the age of 59, 51% by the age of 69 and 74% by the age of 79 (Healy et al. 2008, Lancet, 7, 583-590).

Sergey Brin affected by LRRK2

Google co-founder Sergey Brin has indicated that he is predisposed to PD through a family history and most probably the gene LKKR2 is involved in the same, with the mutation at G2019S.

http://news.cnet.com/8301-1023_3-10045958-93.html

LRRK2 in news

Recently the PD field and specifically the LRRK2 gene came into limelight. The co-founder of Google, Sergy Brin has been diagnosed with PD and preliminary results point out to the fact that there is a point mutation in G2019, where the Glycine residue has been mutated to Serine (S) [G2019S mutation]. This mutation has been linked with enhanced levels of kinase activity and is known to be effected in PD: both in familial (5-6%) and sporadic cases (1-2%).

Brin’s mother was diagnosed with Parkinson’s, and now he has to live with the reality that he might one day develop the disease as well. Says Brin:

Nonetheless it is clear that I have a markedly higher chance of developing Parkinson’s in my lifetime than the average person. In fact, it is somewhere between 20% to 80% depending on the study and how you measure. At the same time, research into LRRK2 looks intriguing (both for LRRK2 carriers and potentially for others).

This leaves me in a rather unique position. I know early in my life something I am substantially predisposed to. I now have the opportunity to adjust my life to reduce those odds (e.g. there is evidence that exercise may be protective against Parkinson’s). I also have the opportunity to perform and support research into this disease long before it may affect me. And, regardless of my own health it can help my family members as well as others.

I feel fortunate to be in this position. Until the fountain of youth is discovered, all of us will have some conditions in our old age only we don’t know what they will be. I have a better guess than almost anyone else for what ills may be mine — and I have decades to prepare for it.


Also more info available at:

http://thegenesherpa.blogspot.com/2008/09/lrrk2-and-parkinson-disease.html

http://news.cnet.com/8301-1023_3-10045958-93.html

LRRK2

LRRK2 (Leucine Rich Repeat kinase 2) is a cytoplasmic protein of 2527 amino acids. This protein is widely expressed in Substantia Nigra (SN) specially in the A9 Dopaminergic neurons (A9 DA). Other regions in the brain where LRRK2 has also been identified include cortex, hippocampus, straitum and cerebellum. Peripheral organs where the existence of LRRK2 has been detected include Heart, Placenta, Kidney, Lung, Skeletal Muscle, Pancreas etc. Subcellular localization of LRRK2 is observed in Golgi, Mitochondira and endosomal vesicles.

As a protein, LRRK2 has both GTPase activity and kinase activity encoded by the same molecule. This is one of the very few proteins found in the human genome which has both the activities in the same gene. The kinase function of LRRK2 has been of utmost importance in PD as it has been observed that enhanced kinase activity of LRRK2 mutants (G2019S, R1441C) leads to neurodegenation and cell death. The kinase domain has reasonale sequence homology to MLK (Mixed Lineage Kinase) subfamily of MAPKKK proteins. How does PD-associated mutant LRRK2 deviate from normal function remains to be elucidated in detail which will in turn help us deduce the normal function of LRRK2 in brains.

alpha-synuclien and LKKR2 in PD

The two most significant genes which have been widely implicated in familial and sporadic PD are the alpha-synuclein (ASN) and Leucine Rich Repeat Kinase 2 (LRRK2). In PD patients with defects in either of gene (through mutation or other disease causing mechansim), evidence of Lewy Bodies (intracellular esinophillic depositions) and Lewy Neurites are observed in the substantia nigra (SN) of the brain.
PD has been the second most common neurodegenerative disease in the world affecting about 2% of the population. It is a neurological disorder in which degeneration of midbrain dopaminergic neurons leads to loss in motor functions.
I would like to define the cardinal symptons of PD as some one who has been "TRAP"-ed by old age:
T: Tremor
R: Rigidity
A: Akinesia / Bradykinesia
P: Postural Instability

Will discuss more about LRRK2 (the gene of my interest) in subsequent posts, and will evolve a link how GPCRs play a role in PD.