Biomedical subjects

M K Dean

Publications and source records attributed to M K Dean.

5 recordsLinked to original sources

PubMed2001

Dimerization of G-protein-coupled receptors.

The evolutionary trace (ET) method, a data mining approach for determining significant levels of amino acid conservation, has been applied to over 700 aligned G-protein-coupled receptor (GPCR) sequences. The method predicted the occurrence of functionally important clusters of residues on the external faces of helices 5 and 6 for each family or subfamily of receptors; similar clusters were observed on helices 2 and 3. The probability that these clusters are not random was determined using Monte Carlo techniques. The cluster on helices 5 and 6 is consistent with both 5,6-contact and 5,6-domain swapped dimer formation; the possible equivalence of these two types of dimer is discussed because this relates to activation by homo- and heterodimers. The observation of a functionally important cluster of residues on helices 2 and 3 is novel, and some possible interpretations are given, including heterodimerization and oligomerization. The application of the evolutionary trace method to 113 aligned G-protein sequences resulted in the identification of two functional sites. One large, well-defined site is clearly identified with adenyl cyclase, beta/gamma and regulator of G-protein signaling (RGS) binding. The other G-protein functional site, which extends from the ras-like domain onto the helical domain, has the correct size and electrostatic properties for GPCR dimer binding. The implications of these results are discussed in terms of the conformational changes required in the G-protein for activation by a receptor dimer. Further, the implications of GPCR dimerization for medicinal chemistry are discussed in the context of these ET results.

Amino Acid Sequence↗

PubMed2001

Lipid-facing correlated mutations and dimerization in G-protein coupled receptors.

A correlated mutation analysis has been performed on the aligned protein sequences of a number of class A G-protein coupled receptor families, including the chemokine, neurokinin, opioid, somatostatin, thyrotrophin and the whole biogenic amine family. Many of the correlated mutations are observed flanking or neighbouring conserved residues. The correlated residues have been plotted onto the transmembrane portion of the rhodopsin crystal structure. The structure shows that a significant proportion of the correlated mutations are located on the external (lipid-facing) region of the helices. The occurrence of these highly correlated patterns of change amongst the external residues suggest that they are sites for protein-protein interactions. In particular, it is suggested that the correlated residues may be involved in either large conformational changes, the formation of heterodimers or homodimers (which may be domain swapped) or oligomers required for activation or internalization. The results are discussed in the light of the subtype-specific heterodimerization observed for the chemokine, opioid and somatostatin receptors.

Amino Acid Sequence↗

PubMed2000

Dimerization and domain swapping in G-protein-coupled receptors: a computational study.

In recent years there has been an increasing number of reports describing G protein-coupled receptor (GPCR) dimerization and heterodimerization. However, the evidence on the nature of the dimers and their role in GPCR activation is inconclusive. Consequently, we present here a review of our computational studies on G protein-coupled receptor dimerization and domain swapping. The studies described include molecular dynamics simulations on receptor monomers and dimers in the absence of ligand, in the presence of an agonist, and in the presence of an antagonist (or more precisely an inverse agonist). Two distinct sequence-based approaches to studying protein interfaces are also described, namely correlated mutation analysis and evolutionary trace analysis. All three approaches concur in supporting the proposal that the dimerization interface includes transmembrane helices 5 and 6. These studies cannot distinguish between domain swapped dimers and contact dimers as the models used were restricted to the helical part of the receptor. However, it is proposed that for the purpose of signalling, the domain swapped dimer and the corresponding contact dimer are equivalent. The evolutionary trace analysis suggests that every GPCR family and subfamily (for which sufficient sequence data is available) has the potential to dimerize through this common functional site on helices 5 and 6. The evolutionary trace results on the G protein are briefly described and these are consistent with GPCR dimerization. In addition to the functional site on helices 5 and 6, the evolutionary trace analysis identified a second functional site on helices 2 and 3. Possible roles for this site are suggested, including oligomerization.

Animals↗

PubMed1991

The prevalence of hepatitis B surface antigen and antibody in home-reared individuals with Down syndrome.

We examined 180 noninstitutionalized persons with Down syndrome for the presence of both hepatitis B surface antigens and antibodies to hepatitis B surface antigen. Two of the 180 subjects with Down syndrome had a positive test. One patient was hepatitis B surface antigen positive and the other was found to have antibodies to hepatitis B surface antigen. Also, 2 of the 155 individuals in the comparison group tested positive for hepatitis B surface antigen. Thus, we did not observe an increased prevalence of hepatitis B surface antigen or antibody in the study group and there was no significant difference between the Down syndrome and comparison groups. This is in contrast to many studies that originated in residential facilities where an increased number of persons with Down syndrome were found to have hepatitis B surface antigenemia. The related public health concerns are discussed.

Adolescent↗

PubMed1991

Thyroid function in Down syndrome.

The thyroid function of 181 patients with Down syndrome was investigated. When compared with a control group of 163 children we found T4 and FT4 levels to be significantly lower and T3 and TSH levels to be significantly higher in the Down syndrome population. Of the 181 patients with Down syndrome, 29 (16%) showed evidence of either uncompensated or compensated hypothyroidism: 11 (6%) had both low T4 and high TSH levels, 14 (8%) had only high TSH values, and 4 (2%) had only low T4 values. One of the patients with Down syndrome had a significantly elevated T4 level. Studying different age groups, we observed a decline of the mean T4, FT4, T3, FT3, and TBG values with advancing age. T4, T3, and TSH blood levels obtained in 1988 were slightly but not significantly lower when compared with values from 1985. Because thyroid dysfunctions in patients with Down syndrome are more common than in the general population, periodic thyroid hormone function tests should be performed in persons with Down syndrome in particular as they advance in age. Thus, individuals with significantly abnormal results can be identified early before clinical symptoms become manifest. If patients with Down syndrome are found to have a thyroid hormone disorder, appropriate treatment should be forthcoming, which in turn will enhance their quality of life.

Adolescent↗