Press releases – August 2019

FRANKFURT. Cultural processes are increasingly short-lived, showing in addition a growing tendency toward self-organisation. As a result, success is now governed by a universal law. This was discovered by the physicists Professor Claudius Gros and Lukas Schneider from Goethe University. Their object of research: 50 years of music charts. 

Since the 1960s, music charts have been compiled using the same criteria - sales profits. Charts therefore provide sets of comparable data spanning many decades, a circumstance that makes them particularly well-suited for the investigation of the long-term development of cultural time scales. This approach is also relevant beyond the cultural domain, in particular with regard to the pace of political opinion formation, which affects the dynamical stability of liberal democracies. 

In a new article published today in Royal Society Open Science, Lukas Schneider and Professor Claudius Gros from the Institute for Theoretical Physics at Goethe University demonstrate that the statistical characteristics, the composition, and the dynamics of the US, UK, Dutch and German pop album charts have changed significantly since the beginning of the 1990s. On the one hand, the diversity of the charts has doubled, or even tripled: Now there are significantly more albums making it to the top 100 or top 40 in a year. On the other hand, we now see that an album either starts off immediately as number one – or never reaches the top. In contrast, from the 1960s to the 1980s, successful albums needed four to six weeks to work their way from their starting position to the top slot. 

 The nature of an album's “lifetime" - the number of weeks an album has been listed – was found to have changed profoundly. Before the 1990s, the statistics of album lifetimes were governed by a Gauss distribution with a logarithmic argument (log normal). Today, the distribution of album lifetimes is characterised in contrast by a power law. The distribution of lifetimes is therefore universal, i.e., independent of the specifics of the process, a key characteristic of the final state of a self-organising process. To explain this development, the authors propose an information-theoretical approach to human activities. The assumption of Schneider and Gros is that humans strive continuously to optimise the information content of their experience and perceptions. Mathematically, information is captured by the Shannon entropy. According to Schneider and Gros, one needs to consider furthermore the Weber-Fechner law, which states that time and other variables are represented and stored in the brain not in a one-to-one ratio, but in a greatly compressed way (on a logarithmic scale). In this view, optimization of the information content of compressed experiences explains the observed chart statistics. 

Overall, the study by Schneider and Gros shows that chart dynamics has accelerated, proceeding today substantially faster than several decades ago. The authors conjecture that a similar acceleration could also be at work for the underlying socio-cultural processes, such as social and political opinion formation. As an earlier work by Gros shows, this could threaten the dynamical stability of modern democracies, as the functioning of democracies is based on reliable temporal ties between electorate and political institutions. These temporal ties are threatened when the time scale of political opinion formation and that of the delayed decision processes drift increasingly apart. (Claudius Gros, Entrenched time delays versus accelerating opinion dynamics: Are advanced democracies inherently unstable? European Physical Journal B 90, 223 (2017). https://epjb.epj.org/articles/epjb/abs/2017/11/b170341/b170341.html )

Publication: Lukas Schneider, Claudius Gros, Five decades of US, UK, German and Dutch music charts show that cultural processes are accelerating, Royal Society Open Science (2019) https://royalsocietypublishing.org/doi/10.1098/rsos.190944 

Further information: Professor Claudius Gros, Institute for Theoretical Physics, Riedberg Campus, telephone: +41 69 798 47818, E-mail gros07@itp.uni-frankfurt.de.

FRANKFURT. In order to control cellular processes and thwart the immune system, the bacterium Legionella pneumophilia, the cause of the notorious Legionnaires' disease, releases hundreds of enzymes. Biochemists at Goethe University have now elucidated important details in the interaction of bacterial effectors. They discovered how the regulatory enzyme SidJ keeps other dangerous virulence factors in check. 

The incidence of Legionnaires' disease has increased in the past two decades. The natural habitat of Legionella is freshwater biotopes, where they mainly reproduce in amoebae. In addition, Legionella can also colonize water tanks or pipes and spread, for example, via poorly maintained air-conditioning systems. Contaminated aerosols are released into the air and trigger the infection. The pathogens cause, among others, pneumonia, which is often fatal in elderly patients or individuals with a weak immune system. 

What makes Legionella so dangerous is its ability to multiply in phagocytes of the immune system by secreting virulence factors. Some of these effectors – the enzymes of what is known as the SidE family – are so toxic that without tight control they would instantly kill their host cells. However, since Legionella needs the host cells in order to multiply, it has developed a sophisticated mechanism for the precise metering of SidE enzyme activity. Details of this process are now reported by scientists at Goethe University and from Grenoble in the journal Nature. 

They have shown that the regulator SidJ also released by Legionella works as an antidote to SidE enzymes, thus ensuring accurate control of SidE activity. The SidJ regulator is a glutamylase, i.e. it has a rare enzyme activity that allows amino acid glutamates to be linked together to form chains. In this case, SidJ attacks the central glutamate of SidE enzymes and inhibits their activity. So far, little is known about glutamylases – so the scientists were all the more surprised when they discovered that it is precisely this type of enzyme which is important for the coordinated interaction of the virulence factors of Legionella. 

“This is a typical example of how completely unpredictable results drive research. Such discoveries are what make science such a fascinating and exciting profession," says Professor Ivan Dikic from the Institute of Biochemistry II and the Buchmann Institute for Molecular Life Sciences at Goethe University. “We can only gain a molecular understanding of the complex world of bacterial infections by working in interdisciplinary teams and combining methods from modern biochemistry and proteomics with cell and structural biology techniques." 

The researchers also revealed how SidJ is activated in host cells: It requires the calcium-binding protein calmodulin found in mammalian cells. Cryo-electron microscopy played an important role in explaining the structure of the calmodulin-SidJ complex. “Glutamylation as a protein modification is understudied. Our finding that Legionella pneumophilia uses exactly this mechanism to sustain the infection certainly argues for more research in this field. For example, the extent to which Legionella utilizes this modification to regulate other cellular processes is completely unclear," explains Dr. Sagar Bhogaraju, who led the microscopic examinations at the European Molecular Biology Laboratory (EMBL) in Grenoble. 

This so far unknown mechanism opens up new possibilities for research to inhibit the spread of Legionella in the host organism. “We're currently working on eliminating SidJ selectively by developing inhibitors for the glutamylase domain. In addition to the use of antibiotics, they could prevent the spread of Legionella pneumophilia in phagocytes," explains Dikic. 

Publication: Sagar Bhogaraju, Florian Bonn, Rukmini Mukherjee, Michael Adams, Moritz M. Pfleiderer, Wojciech P. Galej, Vigor Matkovic, Sissy Kalayil, Donghyuk Shin, Ivan Dikic: Inhibition of SidE ubiquitin ligases through SidJ/Calmodulin catalyzed glutamylation, in Nature 22. Juli 2019 DOI: 10.1038/s41586-019-1440-8 https://www.nature.com/articles/s41586-019-1440-8 

Further information: Professor Ivan Dikic, Institute of Biochemistry II, Niederrad Campus, and Buchmann Institute for Molecular Life Sciences, Riedberg Campus, Tel.: +49(0)69-6301-5964, Email: dikic@biochem2.uni-frankfurt.de.