Biomedical subjects

S Heikkinen

Publications and source records attributed to S Heikkinen.

At least 19 recordsLinked to original sources

PubMed2001

Methods for the measurement of (1)J(NCalpha) and (2)J(NCalpha) from a simplified 2D (13)C(alpha)-coupled (15)N SE-HSQC spectrum.

Two methods for the measurement of (2)J(NCalpha) and (1)J(NCalpha) in (15)N/(13)C-labeled small and medium-size proteins are described. The current approach is based on simplified (13)C(alpha)-coupled (15)N HSQC spectra, where the two (2)J(NCalpha) doublets are separated into two subspectra corresponding to the alpha and beta spin states of the residue's own alpha carbon. The displacement of the two (2)J(NCalpha) doublets between the two subspectra provides an accurate value for (1)J(NCalpha). The alpha/beta filtration is achieved by taking the sum and difference of the recorded complementary in-phase and antiphase J-coupled spectra. J-multiplication is utilized in one of the proposed methods. In this method, an additional coupling evolution period, which is incremented in concert with t(1), is included in the pulse sequence making it possible to scale the peak-to-peak separation.

Humans↗

PubMed2001

Human alpha3-fucosyltransferases convert chitin oligosaccharides to products containing a GlcNAcbeta1-4(Fucalpha1-3)GlcNAcbeta1-4R determinant at the nonreducing terminus.

Human alpha3-fucosyltransferases (Fuc-Ts) are known to convert N-acetyllactosamine to Galbeta1-4(Fucalpha1-3)GlcNAc (Lewis x antigen); some of them transfer fucose also to GalNAcbeta1-4GlcNAc, generating GalNAcbeta1-4(Fucalpha1-3)GlcNAc determinants. Here, we report that recombinant forms of Fuc-TV and Fuc-TVI as well as Fuc-Ts of human milk converted chitin oligosaccharides of 2-4 GlcNAc units efficiently to products containing a GlcNAcbeta1-4(Fucalpha1-3)GlcNAcbeta1-4R determinant at the nonreducing terminus. The product structures were identified by mass spectrometry and nuclear magnetic resonance experiments; rotating frame nuclear Overhauser spectroscopy data suggested that the fucose and the distal N-acetylglucosamine are stacked in the same way as the fucose and the distal galactose of the Lewis x determinant. The products closely resembled a nodulation factor of Mesorhizobium loti but were distinct from nodulation signals generated by NodZ-enzyme.

Acetylglucosamine↗

PubMed2000

Binding of levosimendan, a calcium sensitizer, to cardiac troponin C.

Levosimendan is an inodilatory drug that mediates its cardiac effect by the calcium sensitization of contractile proteins. The target protein of levosimendan is cardiac troponin C (cTnC). In the current work, we have studied the interaction of levosimendan with Ca(2+)-saturated cTnC by heteronuclear NMR and small angle x-ray scattering. A specific interaction between levosimendan and the Ca(2+)-loaded regulatory domain of recombinant cTnC(C35S) was observed. The changes in the NMR spectra of the N-domain of full-length cTnC(C35S), due to the binding of levosimendan to the primary site, were indicative of a slow conformational exchange. In contrast, no binding of levosimendan to the regulatory domain of cTnC(A-Cys), where all the cysteine residues are mutated to serine, was detected. Moreover, it was shown that levosimendan was in fast exchange on the NMR time scale with a secondary binding site in the C-domain of both cTnC(C35S) and cTnC(A-Cys). The small angle x-ray scattering experiments confirm the binding of levosimendan to Ca(2+)-saturated cTnC but show no domain-domain closure. The experiments were run in the absence of the reducing agent dithiothreitol and the preservative sodium azide (NaN(3)), since we found that levosimendan reacts with these chemicals, commonly used for preparation of NMR protein samples.

Calcium↗

PubMed2000

Antibacterial activities of temporin A analogs.

Temporin A (TA) is a small, basic, highly hydrophobic, antimicrobial peptide amide (FLPLIGRVLSGIL-NH2) found in the skin of the European red frog, Rana temporaria. It has variable antibiotic activities against a broad spectrum of microorganisms, including clinically important methicillin-sensitive and -resistant Staphylococcus aureus as well as vancomycin-resistant Enterococcus faecium strains. In this investigation the antimicrobial activity and structural characteristics of TA synthetic analogs were studied. For antibacterial activity against S. aureus and enterococcal strains, the hydrophobicity of the N-terminal amino acid of TA was found to be important as well as a positive charge at amino acid position 7, and bulky hydrophobic side chains at positions 5 and 12. Replacing isoleucine with leucine at amino acid positions 5 and 12 resulted in the greatest enhancement of antibacterial activity. In addition, there was little difference between the activities of TA and its all-D enantiomer, indicating that the peptide probably exerts its effect on bacteria via non-chiral interactions with membrane lipids.

Amino Acid Sequence↗

PubMed2000

Mouse hexokinase II gene: structure, cDNA, promoter analysis, and expression pattern.

In mammalian tissues, the phosphorylation of intracellular glucose to glucose-6-phosphate (Glu-6-P) is facilitated by four distinct hexokinase (HK) isoenzymes, designated as HKI-IV. Because of the role of HKII as a leading glycolytic enzyme in insulin-sensitive tissues such as skeletal muscle, heart, and adipose tissue, defects in HKII function could contribute to the development of insulin resistance and perhaps Type 2 diabetes. As a first step towards elucidation of the physiological role of HKII in insulin resistance and type 2 diabetes using mouse knock-out models, we determined the genomic structure, sequence of the cDNA and of 4.8 kb of the 5' regulatory region, and tissue-specific expression of the mouse HKII gene. The gene comprises 18 exons that span approximately 50 kb of DNA. Nucleotide sequence of the proximal promoter revealed a number of conserved putative transcription factor binding motifs. We also found numerous repeat elements throughout the mouse HKII gene. The mouse HKII cDNA is approximately 5.5 kb in length and contains an open reading frome of 2751 bp encoding a protein of 917 amino acids. The mouse HKII gene is predominantly expressed in skeletal muscle, heart, and adipose tissue. The transcription initiation and polyadenylation sites for the mouse HKII mRNA were similar to those of the rat and human genes.

Animals↗

PubMed2000

Intensity modulated HSQC and HMQC: two simple methods to measure 3J(HNH)alpha in proteins.

Two methods for the measurement of homonuclear 3J(HNH)alpha coupling constants are described. Both HSQC- and HMQC-type experiments employ 'quantitative J-correlation', in which the coupling constant of interest is obtained from the intensity ratio of cross peaks of two spectra. The first spectrum is acquired with 3J(HNH)alpha evolution and the second with alpha-proton decoupling. The resolution of these methods in the F1-domain is not restricted.

Amides↗

PubMed2000

Conformations of the regulatory domain of cardiac troponin C examined by residual dipolar couplings.

Conformations of the regulatory domain of cardiac troponin C (cNTnC) were studied by means of residual dipolar couplings measured from samples dissolved in dilute liquid crystals. Changes in the main chain HN residual dipolar couplings revealed a conformational change in cNTnC due to the complexation with the second binding region (amino acids 148-163) of cardiac troponin I (cTnI). Formation of the complex is accompanied with a molecular realignment in the liquid crystal. The residual dipolar couplings measured for apo-cNTnC and the complex with TnI were in agreement with the values computed from the corresponding closed and open solution structures, whereas for the calcium-loaded conformation the correlation and quality factor were only modest. Ca2+-cNTnC may be subject to conformational exchange. The data support the model that cardiac troponin C functions as a calcium-dependent open-closed switch, such as the skeletal troponin C.

Amino Acid Sequence↗

PubMed1999

Hexokinase II-deficient mice. Prenatal death of homozygotes without disturbances in glucose tolerance in heterozygotes.

Type 2 diabetes is characterized by decreased rates of insulin-stimulated glucose uptake and utilization, reduced hexokinase II mRNA and enzyme production, and low basal levels of glucose 6-phosphate in insulin-sensitive skeletal muscle and adipose tissues. Hexokinase II is primarily expressed in muscle and adipose tissues where it catalyzes the phosphorylation of glucose to glucose 6-phosphate, a possible rate-limiting step for glucose disposal. To investigate the role of hexokinase II in insulin action and in glucose homeostasis as well as in mouse development, we generated a hexokinase II knock-out mouse. Mice homozygous for hexokinase II deficiency (HKII(-/-)) died at approximately 7.5 days post-fertilization, indicating that hexokinase II is vital for mouse embryogenesis after implantation and before organogenesis. HKII(+/-) mice were viable, fertile, and grew normally. Surprisingly, even though HKII(+/-) mice had significantly reduced (by 50%) hexokinase II mRNA and activity levels in skeletal muscle, heart, and adipose tissue, they did not exhibit impaired insulin action or glucose tolerance even when challenged with a high-fat diet.

Adipose Tissue↗

PubMed1999

Gradient BIRDR: a method to select uncoupled magnetization.

The gradient-BIRD-method is an effective way to select 13C-bound protons. By changing the phase of the proton pi-pulse, the same sequence can be used to select protons attached to 12C atoms, i.e., for filtering out the 13C-bound protons. These filters, consisting of single or double gradient-BIRDR clusters (BIRD inversion for remote protons) have considerable filtering bandwidth. Because of the efficient suppression of the coupled magnetization, we implemented the gradient-BIRDR filter in HMBC to replace the conventional low-pass filter.

Carbon Isotopes↗

PubMed1999

J-multiplied HSQC (MJ-HSQC): a new method for measuring 3J(HNHalpha) couplings in 15N-labeled proteins.

A new method for the measurement of homonuclear 3J(HNHalpha) coupling constants in 15N-labeled small proteins is described. The method is based on a modified sensitivity enhanced HSQC experiment, where the 3J(HNHalpha) couplings are multiplied in the f1-dimension. The J-multiplication of homonuclear 3J(HNHalpha) couplings is based on simultaneous incrementation of 15N chemical shift and homonuclear coupling evolution periods. The time increment for the homonuclear coupling evolution period is chosen to be a suitable multiple (2N x t1) of the corresponding increment for 15N-shift evolution. This results in the splitting of the HSQC correlation in the f1-dimension by 2N x 3J(HNHalpha). Because the pulse sequence has good sensitivity and water suppression properties, it is particularly useful for natural abundance samples.

Image Processing, Computer-Assisted↗

PubMed1999

Measurement of homonuclear (2)J-couplings from spin-state selective double-/zero-quantum two-dimensional NMR spectra.

(1)H-detected two-dimensional double-/zero-quantum experiments are described for measurement of homonuclear (2)J(HH)-couplings of NH(2) or CH(2) groups in proteins. These experiments utilize multiple-quantum coherence for determination of the size and the absolute sign of the geminal scalar and dipolar couplings in the presence of broad lines. Spectra are simplified by gradient selection and spin-state selective filters.

Carrier Proteins↗

PubMed1999

Measurement of (1)J(NC') and (2)J(H(N))(C') couplings from spin-state-selective two-dimensional correlation spectrum.

A method for the measurement of (1)J(NC') and (2)J(H(N))(C') coupling constants from a simplified two-dimensional [(15)N, (1)H] correlation spectrum is presented. The multiplet components of the (1)J(NC') doublet in the indirect dimension and (2)J(H(N))(C') in the direct dimension are separated into two subspectra by spin-state-selective filters. Thus each subspectrum contains no more peaks than the conventional [(15)N, (1)H]-HSQC spectrum. Furthermore, the method for the measurement of (1)J(NC') and (2)J(H(N))(C') is designed to exploit destructive relaxation interference (TROSY). The results are verified against the measurements of (1)J(NC') from spin-state-selective [(13)C', (1)H] correlation spectra recorded with additional sequence described here.

Carbon↗

PubMed1999

The codon 64 polymorphism of the beta3-adrenergic receptor gene is not associated with coronary heart disease or insulin resistance in nondiabetic subjects and non-insulin-dependent diabetic patients.

Hyperinsulinemia has been shown to predict coronary heart disease (CHD) events in both nondiabetic subjects and patients with non-insulin-dependent diabetes mellitus (NIDDM). Therefore, defects in genes that regulate insulin action could be responsible for an increased risk of CHD. The Trp64Arg polymorphism of the beta3-adrenergic receptor gene has been linked with abdominal obesity, insulin resistance, and early-onset NIDDM. Therefore, we screened for this polymorphism among 185 unrelated nondiabetic subjects (101 men and 84 women; age, 56+/-1 years [mean +/- SEM]; body mass index [BMI], 27.8+/-0.3 kg/m2) with angiographically confirmed CHD (stenosis > 50% in > or = two coronary arteries), among 119 unrelated patients with NIDDM (90 men and 29 women; age, 62+/-1 years; BMI, 28.7+/-0.4 kg/m2; 95 had CHD by the same criteria and 24 had definite myocardial infarction [MI]), and among 82 healthy men (age, 54+/-1 years; BMI, 26.3+/-0.4 kg/m2) from our previous study. The frequency of the Trp64Arg allele of the beta3-adrenergic receptor gene was similar in nondiabetic patients with CHD (8%), NIDDM patients with CHD (7%), and nondiabetic subjects without CHD (7%). No association was found between cardiovascular risk factors and the codon 64 polymorphism of the beta3-adrenergic receptor gene in patients with CHD. Similarly, this polymorphism was not significantly related to insulin resistance in nondiabetic and NIDDM subjects with CHD evaluated by the euglycemic clamp technique. These results indicate that the Trp64Arg allele of the beta3-adrenergic receptor gene does not contribute to the risk of CHD in nondiabetic subjects and NIDDM patients.

Alleles↗

PubMed1999

NMR assignments, secondary structure, and global fold of calerythrin, an EF-hand calcium-binding protein from Saccharopolyspora erythraea.

Calerythrin is a 20 kDa calcium-binding protein isolated from gram-positive bacterium Saccharopolyspora erythraea. Based on amino acid sequence homology, it has been suggested that calerythrin belongs to the family of invertebrate sarcoplasmic EF-hand calcium-binding proteins (SCPs), and therefore it is expected to function as a calcium buffer. NMR spectroscopy was used to obtain structural information on the protein in solution. Backbone and side chain 1H, 13C, and 15N assignments were obtained from triple resonance experiments HNCACB, HN(CO)CACB, HNCO, CC(CO)NH, and [15N]-edited TOCSY, and HCCH-TOCSY. Secondary structure was determined by using secondary chemical shifts and characteristic NOEs. In addition, backbone N-H residual dipolar couplings were measured from a spin-state selective [1H, 15N] correlation spectrum acquired from a sample dissolved in a dilute liquid crystal. Four EF-hand motifs with characteristic helix-loop-helix patterns were observed. Three of these are typical calcium-binding EF-hands, whereas site 2 is an atypical nonbinding site. The global fold of calerythrin was assessed by dipolar couplings. Measured dipolar couplings were compared with values calculated from four crystal structures of proteins with sequence homology to calerythrin. These data allowed us to recognize an overall similarity between the folds of calerythrin and sarcoplasmic calcium-binding proteins from the sandworm Nereis diversicolor and the amphioxus Branchiostoma lanceolatum.

Amino Acid Sequence↗

PubMed1998

Coherence selection and excitation sculpting using RF-gradients in selective 1D experiments and nonselective 2D experiments

The B0 gradient pulses can be replaced with long high-power pulses (RF-gradients) in z-rotation composite sandwiches. By doing this, practically all B0 gradient-based pulse sequences can be performed with instruments lacking a field gradient accessory. We have implemented RF-gradients into selective 1D and nonselective 2D TOCSY and NOESY experiments. The spectral quality obtained with the RF-gradient method was comparable to that of the B0 method for small- to medium-sized molecules. There are also some advantages in using RF-gradients instead of B0 gradients. There is practically no shift or coupling evolution during RF-gradient pulses. This may be significant in some experiments. Copyright 1998 Academic Press.

Journal Article↗

PubMed1998

Synergistic effect of polymorphisms in uncoupling protein 1 and beta3-adrenergic receptor genes on basal metabolic rate in obese Finns.

The polymorphisms in the uncoupling protein 1 (UCP1, A to G) and beta3-adrenergic receptor (beta3-AR, Trp64Arg) genes have been suggested to be associated with an increased tendency to gain weight. We investigated the frequency of the A to G polymorphism of the UCP1 gene and its effect on basal metabolic rate (BMR) among obese Finns. We also examined the effects of the simultaneous occurrence of the polymorphisms in the UCP1 and beta3-AR genes on BMR. Altogether 170 obese subjects (29 men, 141 women, BMI 34.7beta3.8 kg/m2, age 43+/-8 years, mean+/-SD) participated in the study. The A to G substitution of the UCP1 gene was verified by digestion of the PCR product with Bcl I. The frequency of the A to G polymorphism of the UCP1 gene in obese subjects did not differ significantly from the population-based control subjects (5 vs 1 % for homozygotes (GG) and 35 vs 42 % for heterozygotes (AG), p=0.077, for trend). BMR adjusted for lean body mass, age and sex (adjBMR) was similar among the three UCP1 gene genotypes of obese subjects (AA n=90, AG n=72 or GG n=8). However, the subjects with the polymorphisms in both UCP1 and beta3-AR genes (n=18) had a 79 kcal/day (95% CI 30-128) lower adjBMR than the subjects without these polymorphisms (n=76) (1551+/-77 vs 1629+/-141 kcal/day, p=0.002). Furthermore, adjBMR was 63 kcal/day (95 % CI 7-118 kcal/day) lower in the subjects with both polymorphisms (n=18) compared with the subjects (n=14) who had only the polymorphism in the beta3-AR gene (1551+/-77 vs 1613+/-76 kcal/day, p=0.028). The A to G polymorphism of the UCP1 gene did not have an independent effect on BMR, but its simultaneous existence with the Trp64Arg polymorphism of the beta3-AR gene resulted in more lowered BMR than the Trp64Arg polymorphism of beta3-AR gene alone.

Adult↗

PubMed1998

Different regulation of free fatty acid levels and glucose oxidation by the Trp64Arg polymorphism of the beta3-adrenergic receptor gene and the promoter variant (A-3826G) of the uncoupling protein 1 gene in familial combined hyperlipidemia.

Familial combined hyperlipidemia (FCHL) is characterized by variable expression of dyslipidemias and insulin resistance. Because the genetic background for FCHL is unknown, we investigated the effect of the Trp64Arg polymorphism of the beta3-adrenergic receptor (beta3-AR) gene and the promoter variant A --> G (-3826) of the uncoupling protein 1 (UCP1) gene on glucose and lipid metabolism in FCHL families. Both polymorphisms were screened in 228 members from 27 families with FCHL and in 82 control men from a random population sample. The frequency of the polymorphisms of the beta3-AR and UCP1 genes did not differ between patients with FCHL and controls. Although the rate of insulin-stimulated whole-body glucose uptake evaluated by the euglycemic clamp in family members of patients with FCHL was unaffected by both polymorphisms, subjects with the Trp64Arg genotype of the beta3-AR gene had higher rates of glucose oxidation (17.6+/-4.5 v 15.8+/-4.1 micromol/kg/min, P=.017) and lower levels of free fatty acids (FFAs) in the fasting state (0.56+/-0.27 v 0.61+/-0.28 mmol/L, P=.027) and during the euglycemic clamp (0.12+/-0.10 v 0.21+/-0.15 mmol/L, P=.041) than subjects with the Trp64Trp genotype. We conclude that in FCHL families, codon 64 polymorphism of the beta3-AR gene may influence the rate of glucose oxidation via FFA levels.

Abdomen↗

PubMed1998

Variants of the fatty acid-binding protein 2 gene are not associated with coronary heart disease in nondiabetic subjects and in patients with NIDDM.

OBJECTIVE: To investigate the association of variants of the fatty acid-binding protein (FABP) 2 gene with coronary heart disease (CHD) in nondiabetic subjects and in patients with NIDDM. RESEARCH DESIGN AND METHODS: Cross-sectional study included 135 nondiabetic and 79 NIDDM subjects with stenosis (> 50%) in at least two coronary arteries. A group of 81 healthy nondiabetic men without CHD served as a control population. All exons and intron-exon junctions of the FABP2 gene were amplified with the polymerase chain reaction, and variants were screened with the single-strand conformation polymorphism analysis. RESULTS: The allele frequency of an amino acid polymorphism (alanine-->threonine) in codon 54 of exon 2 of the FABP2 gene was 0.26 in nondiabetic subjects with CHD and 0.27 in NIDDM subjects with CHD. Other variants (GTA 118 GTC, GCGCA-->GCACA in the 3'-noncoding region, and the number of ATT repeats in intron 2) also did not associate with CHD. CONCLUSIONS: The variants of the FABP2 gene are not likely to contribute to the risk of CHD in Finnish nondiabetic and NIDDM subjects.

Alleles↗