Lyme Spirochete Binds to Heparan in Blood Vessels

Borrelia burgdorferi Sticks to Host Cells via Heparin-binding Proteins

A research group at the University of Calgary has watched the binding of fluorescent Borrelia burgdorferi spirochetes, the Lyme disease pathogen, to the surface of blood vessels in mice. (ref. below) A small heparin molecule was shown to block this interaction between the spirochete surface protein BBK32 and the heparan sulfate proteoglycans of the endothelial cells of the skin blood vessels.

The heparin-binding domains in the spirochete protein, BBK32 are easy to spot in the amino acid sequence of this protein that I downloaded from the NCBI protein database:

>gi|19072701|gb|AAL84596.1| BBK32 [Borrelia burgdorferi]
MKKVKSKYLALGLLFGFISCDLFIRYEMKEESPGLFDKGNSILET
SEESIKKPMNKKGKKIARKKGKSKVSRKEPYIHSLKRDSANKSN
FLQKNVILEEESLKTELLKEQSETRKEKIQKQQDEYKGMTQGSL
NSLSGESGELKETIESNEIDITIDSDLRPKSSLQDIAGSNSISYTDE
IEEEDYARYYLDEDDEDDEYYEDDYEEIRLSNRYQSYLEGVKYNV
DSAINTINKIYDTYTLFSTKLTQMYSTRLDNLAKAKAKEEAAKFTK
EDLEKNFKTLLNYIQVSVKTAANFVYINDTHAKRKLENIEAEIKTL
IAKIKEQSNLYEAYKAIVTSILLMRDSLKEVQGIIDKNGVWY
Basic amino acids are K=lysine, R=arginine

The minimal heparin binding pairs, e.g. KKVKSK are shown in red and the strong heparin-binding triplets, e.g. KRK, are shown in blue. Notice that one triplet is augmented with several pairs to further enhance heparin binding.

I would also expect that BBK32 would be internalized into host cells and transported into the nucleus, where it may alter transcription, a la HIV-TAT. The existence of multiple, strong heparin-binding domains may also serve to bind the BBK32 (or the spirochetes) to multiple different heparan sulfate proteoglycans and interfere with the HSPG circulation system. This may have a toxic effect.

reference:
Norman MU, Moriarty TJ, Dresser AR, Millen B, Kubes P, Chaconas G. Molecular mechanisms involved in vascular interactions of the Lyme disease pathogen in a living host. PLoS Pathog. 2008 Oct 3;4(10):e1000169.

The Cause of Allegies and Autoimmune Diseases

Keyhole Limpet Hemocyanin (KLH): Internalized Antigen

Scanning the literature for a common protein that can be used as an experimental antigen, it becomes quickly obvious that a favorite is KLH. This would seem to be an odd choice -- why a keyhole limpet protein? But that is the wrong question.

Why is KLH such a good antigen, i.e. why is it readily presented to the host immune system? If you have been reading my posts, you might be thinking about triplets of basic amino acids and that is the answer.

As soon as I remembered the prominent use of KLH as an antigen, I checked the NCBI protein database and immediately found an unusual KKK (triple lysine) near the amino terminus of hemocyanin II ( it comes in two pieces). This triplet explains why KLH is such a good experimental antigen, because it is internalized into antigen presenting cells by its strong heparin-binding domain. Other components, adjuvants, are typically added to the KLH for injection to make sure that a strong local inflammation occurs.

Autoantigens Have Strong Heparin-Binding Triplet

I also learned that Hashimoto’s thyroiditis is an autoimmune disease mediated by the autoantigen thyroid peroxidase. A quick search reveals that thyroid peroxidase is an autoantigen, because it also has a triplet of basic amino acids that can enhance presentation under inflammatory conditions. Grave’s disease of hyperthyroidism is an autoimmune disease in which the thyroid receptor (with a basic triplet) is an autoantigen. The same kind of triplet of basic amino acids was found when I searched today for fire ant antigens and mosquito antigens.

I have also looked for the triplets in protein databases. The triplets are rare in cytoplasmic and extracellular proteins. The proteins that have triplets are usually identified as autoantigens in some disease. The triplets are common in nuclear proteins, since heparin-binding and nucleic acid-binding share the same basic amino acid domains. The nuclear internalization signal also results in rapid cellular internalization, e.g. HIV-TAT, heparanase, IGF-binding proteins. Nuclear proteins are common autoantigens in lupus.

Inflammation Plus Heparin-Binding Internalization: Allergy, Autoimmunity

Chronic inflammation can produce antibodies against proteins (foreign or self) with strong heparin-binding domains (triplets or sometimes neighboring pairs of basic amino acids, lysine or arginine). The generalization explains why particular proteins in pollens, foods, insects, pets, mites, asthma, MS, lupus, celiac, etc. produce antibody responses.

HIV TAT and Methamphetamine -- TNF

HIV infection and methamphetamine both cause inflammation of the brain and together they are paralyzing.

What’s worse than a TNF typhoon resulting from methamphetamine use? The answer is a TNF typhoon resulting in dementia from HIV infection of the brain.
Combine methamphetamine with HIV in the brain and the result is a Parkinson’s type of paralysis.

This sounds like very morbid subject matter to pursue out of curiosity, but if you put heparin into the equation, as I always do, it all becomes very interesting.

Here are pieces to the big picture:

HIV, the AIDS virus, infects cells of the immune system and causes chronic inflammation. The inflammation causes a disruption of heparin metabolism and since heparin is a major part of the matrix that holds together the endothelial cells that line the capillaries that feed the brain, the capillaries leak, i.e. there is a leak in the blood brain barrier. HIV-infected cells can pass out of the capillaries and into the brain. Here comes the insidious part, HIV produces a protein called TAT.

I drew a graphic of TAT with the basic amino acids in blue. The sequence of this nasty little protein shows how it gets around. It is secreted from cells, attached to heparan sulfate proteoglycans. It sticks tightly to heparin (yellow and red stick figures, sticking to ribbon of TAT), because of the patches with three and four adjacent basic amino acids. Frequently, the TAT will just be secreted and then sweep over the surface of the infected cell and be brought back into the cell on the circulating HSPG.

DPVDPNIEPWNHPGSQPKTACN
RCHCKKCCYHCQVCFIKKGLGI
SYGRKKRRQRRRPSQGGQTHQ
DPIPKQPSSQPRGDPTGPKE

A protein with three adjacent basic amino acids will get swept into a cell. All allergens that I have examined have this internalization triplet of basic amino acids. TAT is so powerful, that if it is chemically linked to the larger fluorescent protein from jelly fish (left with green, fluorescent amino acid derivative down the center), the whole fluorescent protein is dragged into cells.

The TAT can move from the HSPGs of an HIV-infected cell to neighboring cells with HSPGs. The TAT then gets taken into the cytoplasm of the next cell. Four adjacent basic amino acids are the signal that transports a protein to the nucleus and into the nucleus. It is in the nucleus that TAT really causes trouble. The TAT can move from an infected immune cell in the brain to neurons. TAT can kill neurons and stimulate other cells to produce TNF.

Methamphetamine also causes a TNF storm in the brain. This is a quick way to start the wasting symptoms that TNF in known for -- it is also call cachexin, after the wasting process of cachexia. If methamphetamine is given to someone with neurological symptoms of HIV, then the neuropathology is further exaggerated into a Parkinson’s type of paralysis. The TNF production of both is additive.

TNF production by methamphetamine brings up the consequences of the very closely related compound amphetamine (Adderall, Dexedrine) used by children and young adults (college age) as a treatment for ADHD.

reference:
Theodore S, Cass WA, Nath A, Maragos WF. 2007. Progress in understanding basal ganglia dysfunction as a common target for methamphetamine abuse and HIV-1 neurodegeneration. Curr HIV Res. May;5(3):301-13.