Midlands State University Medical School Staff Publications
https://zdhr.uz.ac.zw/xmlui/handle/123456789/599
2024-03-28T16:27:29ZCalcium is the molecular switch shifting the phytosulfokine receptor 1 (PSKR1) from kinase to guanylate cyclase activity
https://zdhr.uz.ac.zw/xmlui/handle/123456789/603
Calcium is the molecular switch shifting the phytosulfokine receptor 1 (PSKR1) from kinase to guanylate cyclase activity
Conference presentation; Many plant responses are mediated by interactions between intracellular calcium and the second messenger cGMP formed by guanylate cyclases (GCs). Previously we identified a novel class of receptor-GCs containing the GC catalytic center embedded within the kinase domain and showed that the recombinant cytoplasmic domain of phytosulfokine receptor AtPSKR1 has both guanylate cyclase and kinase activity in vitro (Kwezi et al. 2011 J Biol Chem 286: 22580-8). We now show that physiological increases in calcium levels enhance GC activity of AtPSKR1 whereas these calcium levels reversibly inhibit kinase activity. In addition PSKR1 kinase activity is reduced in the presence of the GC product cGMP. Recombinant AtPSKR1 can undergo in vitro autophosphorylation and we have confirmed it has 14 phosphorylation sites in its cytoplasmic domain including 8 serine, 3 threonine and 3 tyrosine residues. Three phospho-serine residues at the juxta-membrane position were mutated to either mimic phosphorylation on or off states. Kinase activity was enhanced in the on mutant and suppressed in the off mutant while GC activity was unaffected suggesting calcium acts as a molecular switch of PSKR1- mediated signalling that can be modulated by the phosphorylation state. The challenge now lies in understanding how molecular interactions between the GC and kinase domains are capitalized on in the plant.
A Dimeric Calcium-modulated GC-linked Receptor Kinase, PSKR1
https://zdhr.uz.ac.zw/xmlui/handle/123456789/604
A Dimeric Calcium-modulated GC-linked Receptor Kinase, PSKR1
Abstract; The phytosulfokine receptor 1, PSKR1 is a membrane-localised leucine-rich repeat receptor-like kinase that also possesses intrinsic guanylate cyclase (GC) activity. The GC activity is conferred, in part, by the presence of a GC catalytic centre that is embedded within its kinase domain. This unusual domain architecture represents a novel class of GC-linked receptor kinases. This novel class of kinases was unearthed using sequence homology-guided bioinformatic data mining tools. Only four members of this new class of kinases have been shown to possess both kinase and GC activity. Currently, there is a paucity of information as to how this dual catalytic activity is regulated in these molecules; therefore we set out to explore the regulatory factors that modulate the dual catalysis in this unusual family of receptor kinases. Our functional studies on PSKR1 demonstrate that calcium acts as a molecular switch regulating this dual catalysis. Functional analysis of PSKR1 at different calcium concentrations showed that calcium inhibits the kinase activity of PSKR1 in a concentration dependant manner whilst on the other hand, enhancing the GC activity of PSKR1. Our previous studies have also demonstrated that, cyclicGMP (a product of GC activity) inhibits the kinase activity of PSKR1. Taken together, our observations indicate that calcium and cyclicGMP act as molecular switches of PSKR1-mediated signalling. Furthermore, our structural analysis of the cytoplasmic domain of PSKR1 suggests that it exists as a reversible dimer in solution. This observation may represent a physiological conformation of PSKR1. In a separate experiment, using tandem mass spectrometry, we have mapped out the phosphorylation pattern of the cytoplasmic domain of PSKR1. Our findings show that the cytoplasmic domain of PSKR1 has 14 phosphorylation sites in its cytoplasmic domain including 3 phospho-tyrosines. This current study presents a mechanistic model of how calcium and phosphorylation act as bimodal switches regulating the dual catalysis in PSKR1.
Estimated glomerular filtration rate and C-reactive protein measures enhance the specificity for left ventricular hypertrophy detection using electrocardiographic criteria: paper presented at the 4th Congress of the African Federation of Clinical Chemists; Zimbabwe: 28-30 April 2015
https://zdhr.uz.ac.zw/xmlui/handle/123456789/602
Estimated glomerular filtration rate and C-reactive protein measures enhance the specificity for left ventricular hypertrophy detection using electrocardiographic criteria: paper presented at the 4th Congress of the African Federation of Clinical Chemists; Zimbabwe: 28-30 April 2015
Introduction: Left ventricular hypertrophy (LVH), the detection of which is recommended for routine risk prediction by all guidelines, is more prevalent in groups of African ancestry. This is in-part attributed to higher prevalence rates of obesity. The detection of LVH using standard electrocardiographic (ECG) criteria (ECG-LVH) has poor sensitivity and specificity and therefore needs modification in groups of African ancestry.
Aim: To assess the usefulness of independent associations between Left Ventricular Mass Index (LVMI) and estimated glomerular filtration rate (eGFR) or serum C-reactive protein (CRP) concentrations to complement ECG criteria for LVH detection in predominantly obese African populations.
Method: LVH determined by ECG using at least 12 different criteria (formulae) was compared to LVH determined by echocardiography (LV mass index>51g/m2.7) in a random sample of 358 participants from a prospective cohort from an urban, developing community of African ancestry in South Africa (41% obese) and used together with CRP concentrations and eGFR above or below the median for the sample.
Results: A combination of CRP concentrations and eGFR above or below the median for the sample respectively showed significant performance (AUC=0.61±0.03, p<0.0005), but a low specificity (ability to report negative results as negative) for LVH detection (77%). When eGFR and CRP concentrations were employed to complement the R wave amplitude of the electrocardiographic lead aVL (RaVL)the specificity increased (93%), although the overall performance did not improve (AUC=0.71±0.03, p<0.0005, RaVL alone: AUC=0.70±0.03). The sensitivity (ability to report positive results as positive) of 25% was however in-line with previously reported sensitivities for LVH detection using ECG criteria in alternative population samples. However, without changing overall performance, eGFR together with RaVL increased the specificity to 88% and CRP concentrations when considered together with RaVL increased the specificity to 87%.
Summary: Routine measurements of CRP and GFR can be used to enhance the specificity of electrocardiographic tests for LVH (especially the RaVL criterion) in obese African patients since these exhibit poor results from ECG alone.
Conclusion: In groups of African ancestry, obesity contributes toward a poor validity and performance of all voltage criteria for the detection of LVH, but the use of eGFR and/or CRP concentrations to complement ECG criteria increases the specificity without altering the overall performance. Learning Outcomes: This study reveals the extra importance and usefulness of routine clinical laboratory tests in enhancing specialist diagnostic procedures.
Anxiolytic activity of a Boophone disticha: Behavioral analysis in mice subjected to early maternal separation followed by later stressors: paper presented at the International summit on past and present research systems of green chemistry;August 25-27, 2014 Hilton Philadelphia Airport, USA
https://zdhr.uz.ac.zw/xmlui/handle/123456789/601
Anxiolytic activity of a Boophone disticha: Behavioral analysis in mice subjected to early maternal separation followed by later stressors: paper presented at the International summit on past and present research systems of green chemistry;August 25-27, 2014 Hilton Philadelphia Airport, USA
Paper presented at the International summit on past and present research systems of green chemistry;August 25-27, 2014 Hilton Philadelphia Airport, USA; Background: Boophone disticha is one of the commonly used bulbous plants in the treatment of anxiety disorders by indigenous people of Zimbabwe and surrounding countries but there is currently lack of scientific evidence for such claims. Therefore, the current study aimed to evaluate the anxiolytic efficacy of B. disticha aqueous ethanolic extract in adult Onincis France I(OFI) mice subjected to early life stress followed by later stressors.
Methods: OFI mice were assigned to two groups at birth. Group Amice (control) were left undisturbed during stress procedures while Group B litter (MS+FS) was subjected to three hours daily maternal separation (MS) from PND2 to PND14,followed subsequently with twenty minutes of forced swim stress (FS) during adolescence (on PND35) and adulthood (on ND60 and PND90). On PND91, thirty MS+FS mice from Group B were randomly assigned to five groups (B1-B5; n=6 each) for further treatments. Group A (n=6) and Group B1 mice were given six daily oral doses from PND92-97 of normal saline (vehicle); Group B2received diazepam, 1mg/kg body weight (BW); whilst Group B3, B4and B5were given low, medium and high dose of B. disticha extract at dosages of 10, 25 and 40 mg/kg BW respectively. On PND98, the open field and elevated plus maze tests were used to obtain psychopharmacological properties of B. disticha.
Results: Mice subjected to repeated early MS and subsequent FS during adulthood showed robust phenotypic abnormalities as compared to control undisturbed littermates, suggestive of increased anxiety-like behavior and inhibited exploratory locomotion. The benzodiazepine receptor agonist diazepam (1 mg/kg) produced a significant anxiolytic-like effect in the open field and elevated plus maze in stressed anxious mice. Current results found that stressed Mice treated with B. disticha aqueous extract also expressed lower scores of anxiety-like behaviors and higher exploratory and locomotor activities than the vehicle treated group.
Conclusions: The present findings demonstrate that abnormal anxiety-like and exploratory behavioral phenotypes in stressed mice are sensitive to diazepam and suggest that B. disticha is also effective in ameliorating these abnormalities.