Regulatory protein interactions are commonly attributed to lock-and-key associations that bring interacting domains together. However, studies in some systems suggest that regulation is not achieved by binding interactions alone. We report our investigations on specific physical characteristics required of the Hsp40 J-domain to stimulate ATP hydrolysis in the Hsp40-Hsp70 molecular chaperone machine. Biophysical analysis using isothermal titration calorimetry, and nuclear magnetic resonance spectroscopy reveals the importance of helix rigidity for the maintenance of Hsp40 function. Our results suggest that the functional J-domain acts like a semi-elliptical spring, wherein the resistance to bending upon binding to the Hsp70 ATPase modulates the ATPase domain conformational change and promotes ATP hydrolysis.

Small monomeric proteins often fold in apparent two-state processes with folding speeds dictated by their native-state topology. Here we test, for the first time, the influence of monomer topology on the folding speed of an oligomeric protein: the heptameric cochaperonin protein 10 (cpn10), which in the native state has seven ␤-barrel subunits noncovalently assembled through ␤-strand pairing. Cpn10 is a particularly useful model because equilibrium-unfolding experiments have revealed that the denatured state in urea is that of a nonnative heptamer. Surprisingly, refolding of the nonnative cpn10 heptamer is a simple two-state kinetic process with a folding-rate constant in water (2.1 sec −1 ; pH 7.0, 20°C) that is in excellent agreement with the prediction based on the native-state topology of the cpn10 monomer. Thus, the monomers appear to fold as independent units, with a speed that correlates with topology, although the C and N termini are trapped in ␤-strand pairing with neighboring subunits. In contrast, refolding of unfolded cpn10 monomers is dominated by a slow association step.Keywords: cochaperonin protein; protein folding; protein assembly; contact order; topology Many small monomeric proteins fold in apparent two-state processes, whereas folding of larger such proteins (of >100 residues) often require involvement of equilibrium and kinetic intermediates (Jackson 1998). Statistical correlations of the folding rates of small single-domain proteins (folding without intermediates) against a number of parameters, such as stability, chain length, transition-state placement, and topology, have been tested. The native-state contact order, a parameter reporting on the degree of local versus nonlocal contacts in the native state (i.e., a measure of the native-state topology), was found to be highly significant (Plaxco et al. 1998(Plaxco et al. , 2000. Contact order is defined as the average sequence separation between contacting residues in the native state. Proteins with lower contact order (greater influence of local interactions, such as ␣-helices) exhibit an increased folding rate compared with that of proteins with higher contact order (greater influence of nonlocal interactions, such as ␤-sheets). Also related to native-state topology, the number of sequence-distant contacts per residue, defined as the long-range order (LRO), correlates as well as contact order with experimental folding rates of small globular proteins (Gromiha and Selvaraj 2001;Gromiha 2003): The more sequence-distant contacts per residue, the slower the folding is.Several groups have attempted to define mechanistic models that explain the empirical topology-rate correlation. The topomer-search model is a simple mechanistic description that quantitatively accounts for the broad scope of observed two-state folding rates (with one notable exception; Jones and Wittung-Stafshede 2003). This theory stipulates that the search for those unfolded conformations with a grossly correct topology is the rate-limiting step in folding (Makarov a...

Thirty years ago a class of proteins was found to prevent the aggregation of Rubisco. These proteins’ ability to prevent unwanted associations led to their being called chaperones. These chaperone proteins also increased in expression as a response to heat shock, hence their label as heat shock proteins (Hsps). However, neither label encompasses the breadth of these proteins’ functional capabilities. The term “unfoldases” has been proposed, as this basic function is shared by most members of this protein family. Onto this is added specializations that allow the different family members to perform various cellular functions. This current article focuses on the resolved structural bases for these functions. It reviews the currently available molecular structures in the Protein Data Bank for several classes of Hsps (Hsp60, Hsp70, Hsp90, and Hsp104). When possible, it discusses the complete structures for these proteins, and the types of molecular machines to which they have been assigned. The structures of domains and the associated functions are discussed in order to illustrate the rationale for the proposed unfoldase function.

The spread of the corona virus around the world has spurred travel restrictions and community lockdowns to manage the transmission of infection. In the Philippines, with a large population of overseas Filipino contract workers (OFWs), as well as foreign workers in the local online gaming industry and visitors from nearby countries, the first reported cases were from a Chinese couple visiting the country in mid-January 2020. Three months on, by mid-March, the COVID-19 cases in the Philippines had reached its first 100, before it exploded to the present 178,022 cases (as of August 20, 2020). Here, we report a genomic survey of six (6) whole genomes of the SARS-CoV-2 virus collected from COVID-19 patients seen at the Philippine General Hospital, the major referral hospital for COVID-19 cases in Metro Manila at about the time the Philippines had over a hundred cases. Analysis of commonly observed variants did not reveal a clear pattern of the virus evolving towards a more infectious and severe strain. When combined with other available viral sequences from the Philippines and from GISAID, phylogenomic analysis reveal that the sequenced Philippine isolates can be classified into three primary groups based on collection dates and possible infection sources: (1) January samples collected in the early phases of the pandemic that are closely associated with isolates from Wuhan, China; (2) March samples that are mainly linked to the M/V Diamond Princess Cruise Ship outbreak; and (3) June samples that clustered with European isolates, one of which already harbor the globally prevalent D614G mutation which initially circulated in Europe. The presence of community-acquired viral transmission amidst compulsory and strict quarantine protocols, particularly for repatriated Filipino workers, highlights the need for a refinement of the quarantine, testing, and tracing strategies currently being implemented to adapt to the current pandemic situation.

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