Researchers in Florida are reporting an advance toward tapping the enormous potential of an emerging new group of antibiotics identical to certain germ-fighting proteins found in the human immune system.  Their study, which may help fight the growing epidemic of drug-resistant infections, is in the current (August) issue of ACS’ Biomacromolecules, a monthly journal.

In the new study, D. Matthew Eby, Glenn Johnson, and Karen Farrington point out that scientists have long eyed the germ-fighting potential of antimicrobial peptides (AMPs).  These small proteins fight a wide range of bacteria and fungi in the body and have the potential to be developed into powerful drugs to overcome infections that are resistant to conventional drugs.  But scientists report difficulty producing effective AMPs because the antibiotics are fragile and easily destroyed in the body.  An effective way to stabilize them is needed, they say.

In laboratory studies, the researchers showed that the coating protected the antibiotics from destruction by other chemicals while allowing the release of a controlled antibiotic dose for an extended period of time.  These features are key to the effective use of AMPs as antibiotics, they say.

A small molecule that locks an essential enzyme in an inactive form could one day form the basis of a new class of unbeatable, species-specific antibiotics, according to researchers at Fox Chase Cancer Center.

Their findings, highlighted on the cover of the June 23 issue of the journal Chemistry & Biology, take advantage of an emerging body of science regarding “morpheeins” – proteins made from individual components that are capable of spontaneously reconfiguring themselves into different shapes within living cells.

The researchers discovered a small molecule, which they have named morphlock-1, binds the inactive form of a protein known as porphobilinogen synthase (PBGS), an enzyme used by nearly all forms of cellular life.  The functioning form of PBGS is built from eight identical component parts – in what is called an octamer configuration – and is essential among nearly all forms of life in the processes that enable cells to use energy.  The other configuration is made of six parts – or a hexamer configuration – and serves as a “standby” mode for the protein.

“As the name suggests, morphlock-1 essentially locks the hexamer configuration into place, preventing its protein subunits from reconfiguring into the active assembly,” says lead investigator Eileen Jaffe, Ph.D, a Senior Member of Fox Chase.  “Targeting morpheeins in their inactive assemblies provides an entirely new approach to drug discovery.”

While their study was performed using a pea plant-version of PBGS, the researchers have reason to believe the principle could apply to bacterial versions of PBGS as well.  “Using morphlock-1 as a base, we are seeking to fine tune the molecule so that it blocks just the bacterial version of the PBGS enzyme, ” Jaffe says.

“Because PBGS is so crucial for life, the part of the enzyme where chemistry happens is highly conserved through evolution,” Jaffe says, meaning that an all-around PBGS-inhibiting drug would harm bacteria, peas and people alike.  The area where the potential drug binds to the hexamer form of the protein, however, has been found to differ among species, depending how far the organisms have evolved from each other.

When PBGS is in its inactive hexamer form, there is a small cavity on the surface of the assembled complex.  Using computer docking techniques, Jaffe and her Fox Chase colleagues identified a suite of small molecules predicted to bind to this cavity.

The researchers then bought and tested a selection of these molecules in the lab to see if any of them stabilized the pea PBGS in its hexamer assembly.  One inhibitor in particular, given the name morphlock-1, potently drove the formation of the hexamer in pea PBGS, but not in that of humans, fruit flies, or the infectious bacteria Pseudomonas aeruginosa, or Vibrio cholerae, the latter of which causes cholera.  Morphlock-1 is a potent inhibitor of pea PBGS, but not of the PBGS from these other organisms.

Jaffe coined the term “morpheein” in 2005 after a study of the structure of PBGS revealed its shape-shifting tendencies.  While initially met with skepticism because the existence of morpheeins contradicts some classic concepts about protein structure and function, subsequent studies have reinforced that PBGS (and perhaps other proteins) exhibits this behavior.  According to Jaffe, this study is the first to make use of alternate morpheein shapes as a potential strategy for drug discovery, in general, particularly for antibiotics.

“Multi-drug resistance drives the need for developing new antibiotics,” Jaffe says.  “Since drugs that stabilize the inactive PBGS hexamer need not be chemically similar to each other, it will be difficult for the bacterium to develop complete resistance to a cocktail of such compounds.”

New research into the toxins, virulence, spread and prevention of the superbug Clostridium difficile is reported in the June special issue of the Journal of Medical Microbiology. These findings will play a crucial role in providing us with ammunition in the fight against a sometimes deadly pathogen.

Clostridium difficile is found in the environment but is most common in hospitals. It can cause a serious hospital-acquired infection when antibiotics are used as they upset the balance of the normal gut flora, allowing C. difficile to grow and produce toxins. It is carried in the guts of 3% of healthy humans but carriage rates in hospital patients tend to be much higher and elderly people in hospitals, being treated with antibiotics are most at risk of developing infection. The bacteria produce spores when they encounter unfavourable conditions. Transmission of infection is through the ingestion of these spores which can survive on surfaces and floors for years and are resistant to many disinfectants and antiseptics, including alcohol hand gel.

Symptoms include diarrhoea, nausea, abdominal pain, loss of appetite, fever, bowel inflammation and possible perforation, which can be fatal. Only two antibiotics are regularly used to treat C. difficile infection: metronidazole and vancomycin, but relapse is a common problem following treatment. In 2004, a hypervirulent strain (C. difficile 027/NAP1/BI) was reported, which appears to make toxins more rapidly and at higher levels than other strains, as well as being resistant to many antibiotics, including fluoroquinolones.

Several studies in the Journal of Medical Microbiology look at the spread of C. difficile in different countries, including Austria and Korea. Research shows that the use of antibiotic increased the risk of outbreaks of the hypervirulent strain of C. difficile in the Netherlands. The issue also contains evidence to suggest that C. difficile could be spread between animals and humans – researchers have isolated the bacterium from food animals in Slovenia.

Scientists investigated the effects of antibiotics, antigens and other agents on the virulence and pathogenicity of C. difficile. Toxins were also studied; research reveals some important information about the synthesis, processing and effects of different toxins. A new gene sequence has been discovered in the hypervirulent C. difficile 027 strain, which could be related to its increased virulence by affecting toxin binding.

The potential for a ‘designer’ probiotic for C. difficile is discussed. Professor Ian Poxton, former Editor-in-Chief of the Journal of Medical Microbiology said “this is an important approach that is hopefully much better than previously reported studies using commercially available yoghurt-like drinks, and certainly more palatable than ‘faecal transplants’.”

Researchers from the John Innes Centre and the University of East Anglia have recently elucidated the structure and function of an enzyme which is involved in decorating antibiotics with sugar molecules. Many antibiotics have a variety of different carbohydrate molecules attached to them which can help the antibiotic to be taken up by the target organism or overcome resistance. By manipulating the sugar, it may be possible to restore usefulness in antibiotics to which resistance has developed.

The aim of this research was to find out how these sugars are made, and how their structures affect their biological activity. The researchers studied an enzyme from a little studied species of Streptomyces bacteria, which produces the antibiotic tylosin. The enzyme they looked at is involved in making a sugar molecule that decorates tylosin. By working out how the carbohydrates are made, it may be possible to make unnatural sugars, with different properties.

“This is a bit of biochemistry we can’t do with chemistry. We need to go back to the fundamentals of how these sugars are put together in nature”, said Professor Rob Field. “We want to see what happens when we decorate an antibiotic with sugar and which sugars make the best decoration.”

They are not yet near to a market product, but trying to understand at a fundamental level how these sugars are made. “We are still putting the toolkit together” said Professor Field. By modelling the enzyme, and comparing it with related enzymes, they have been able to identify the key parts needed for its function, and propose the biochemical basis for how it creates the carbohydrate’s precise st