Biology subjects

Mäkelä, J.

Publications and source records attributed to Mäkelä, J..

3 recordsLinked to original sources

bioRxiv2026

Bacterial Hsp70 DnaK transiently samples the proteome to rapidly capture stress-induced misfolding

Protein-quality-control systems are essential for cells to maintain protein homeostasis during both steady-state growth and acute stress. Yet, how protein chaperone engagement dynamically changes as proteostasis demand increases remains poorly understood. Here, we combine rapid temperature control with single-molecule tracking to follow the bacterial heat shock protein 70 (Hsp70) DnaK in live Escherichia coli. We found that most DnaK molecules actively engage with the proteome already at the optimal growth temperature, rather than form a freely diffusing reserve. Acute heat shock reallocates the DnaK pool within seconds primarily increasing the lifetime but also frequency of client engagements. Perturbing the chaperone network reveals that this redistribution reflects proteostasis demand and network capacity: loss of small heat shock proteins IbpAB drives prolonged DnaK engagement and limits recovery, whereas overexpression of thermolabile proteins alone can produce heat shock-like dynamics. Together, our findings reveal how chaperones are dynamically reallocated during proteotoxic stress and establish DnaK mobility as a sensitive readout of proteostasis demand.

cell biology↗

bioRxiv2026

Pathogenic PTCD1 variants cause mitochondrial protein aggregation and cardiomyopathy

Disorders of mitochondrial oxidative phosphorylation affecting multiple respiratory chain complexes are among the most common causes of mitochondrial disease in humans. However, impaired energy metabolism alone does not fully account for tissue-specific vulnerability and disease progression, suggesting that additional molecular mechanisms contribute to disease pathology. We previously identified PTCD1 variants in a child with infantile cardiomyopathy associated with a combined respiratory chain deficiency. Here, we establish the pathogenicity of three PTCD1 (NM_015545.4) variants in which p.(Arg113Trp) and p.(Gly184Arg) segregate in cis whereas p.(Arg130*) is present in trans, demonstrating that disrupted mitochondrial proteostasis contributes to tissue damage in PTCD1 deficiency. PTCD1 patient cardiac tissue characterisation revealed impaired mitoribosome biogenesis, alongside increased aggregation of selective mitochondrial matrix proteins. Cell models expressing individual and combined PTCD1 missense variants, coupled with proteomics, recapitulated the protein aggregation, with the cis p.(Arg113Trp);p.(Gly184Arg) combination showing the most severe effect. Protein aggregation was accompanied by altered OPA1 processing and mitochondrial network remodelling. Our findings establish accumulating proteotoxic stress arising from impaired mitoribosome assembly as a pathogenic mechanism in post-mitotic tissues, driving PTCD1 cardiomyopathy.

cell biology↗

bioRxiv2019

The SMC complex, MukBEF, organizes the Escherichia coli chromosome by forming an axial core

Structural Maintenance of Chromosomes (SMC) complexes organize and individualize chromosomes ubiquitously, thereby contributing to their faithful segregation. Here we explore how Escherichia coli chromosome organization emerges from the action of the SMC complex MukBEF, using quantitative imaging in cells with increased MukBEF occupancy on the chromosome. We demonstrate that the E. coli chromosome is organized as series of loops around a thin axial MukBEF core whose length is ~1100 times shorter than the chromosomal DNA. The core is linear (1 m), or circular (1.5 m) in the absence of MatP, which displaces MukBEF from the 800 kbp replication termination region (ter). Our findings illustrate how MukBEF compacts the chromosome lengthwise and demonstrate how displacement of MukBEF from ter promotes MukBEF enrichment with the replication origin.

cell biology↗