Sexual dimorphism in relation to adipose tissue and intrahepatocellular lipid deposition in early infancy.

Sexual dimorphism in adiposity is well described in adults, but the age at which differences first manifest is uncertain. Using a prospective cohort, we describe longitudinal changes in directly measured adiposity and intrahepatocellular lipid (IHCL) in relation to sex in healthy term infants. At median ages of 13 and 63 days, infants underwent quantification of adipose tissue depots by whole-body magnetic resonance imaging and measurement of IHCL by in vivo proton magnetic resonance spectroscopy. Longitudinal data were obtained from 70 infants (40 boys and 30 girls). In the neonatal period girls are more adipose in relation to body size than boys. At follow-up (median age 63 days), girls remained significantly more adipose. The greater relative adiposity that characterises girls is explained by more subcutaneous adipose tissue and this becomes increasingly apparent by follow-up. No significant sex differences were seen in IHCL. Sex-specific differences in infant adipose tissue distribution are in keeping with those described in later life, and suggest that sexual dimorphism in adiposity is established in early infancy.

The diabetic pregnancy and offspring blood pressure in childhood: a systematic review and meta-analysis.

AIMS/HYPOTHESIS: Offspring of diabetic mothers have increased risk of the metabolic syndrome in adulthood. Studies examining BP in offspring of diabetic mothers have conflicting conclusions. We performed a systematic review and meta-analysis of studies reporting offspring BP in children born to diabetic mothers. METHODS: Citations were identified in PubMed. Authors were contacted for additional data. Systolic and diastolic BP in offspring of diabetic mothers and controls were compared. Subgroup analysis of type of maternal diabetes and offspring sex were performed. Fixed-effects models were used, and random-effects models where significant heterogeneity was present. Meta-regression was used to test the relationship between offspring systolic BP and prepregnancy BMI. RESULTS: Fifteen studies were included in the review and 13 in the meta-analysis. Systolic BP was higher in offspring of diabetic mothers (mean difference 1.88 mmHg [95% CI 0.47, 3.28]; p = 0.009). Offspring of mothers with gestational diabetes had similar diastolic BP to controls, but higher systolic BP (1.39 mmHg [95% CI 0.00, 2.77]; p = 0.05); results for type 1 diabetes were inconclusive and there were no separate data available on offspring of type 2 diabetic mothers. Male offspring of diabetic mothers had higher systolic BP (2.01 mmHg [95% CI 0.93, 3.10]; p = 0.0003) and diastolic BP (1.12 mmHg [95% CI 0.36, 1.88]; p = 0.004) than controls; in female offspring there was no difference (systolic: 0.54 mmHg [95% CI -1.83, 2.90], p = 0.66; diastolic: 0.51 mmHg [95% CI -1.07, 2.09], p = 0.52). The correlation between offspring systolic BP and maternal prepregnancy BMI was not significant (p = 0.37). CONCLUSIONS/INTERPRETATION: Offspring of diabetic mothers have higher systolic BP than controls. Differences related to sex and type of maternal diabetes require further investigation.

The diabetic pregnancy and offspring BMI in childhood: a systematic review and meta-analysis.

AIMS/HYPOTHESIS: Offspring of mothers with diabetes are at increased risk of metabolic disorders in later life. Increased offspring BMI is a plausible mediator. We performed a systematic review and meta-analysis of studies examining offspring BMI z score in childhood in relation to maternal diabetes. METHODS: Papers reporting BMI z scores for offspring of diabetic (all types, and pre- and during-pregnancy onset) and non-diabetic mothers were included. Citations were identified in PubMed; bibliographies of relevant articles were hand-searched and authors contacted for additional data where necessary. We compared offspring BMI z score with and without adjustment for maternal pre-pregnancy BMI. We performed fixed effect meta-analysis except where significant heterogeneity called for use of a random effects analysis. RESULTS: Data were available from nine studies. In the diabetic group unadjusted mean offspring BMI z score was 0.28 higher (all diabetic mothers vs controls (95% CI 0.09, 0.47; p = 0.004; nine studies; offspring of diabetic mothers n = 927, controls n = 26,384) and with adjustment for maternal pre-pregnancy BMI, 0.07 higher (95% CI -0.15, 0.28; p = 0.54; three studies; offspring of diabetic mothers n = 244, controls n = 11,206). There was no evidence of a difference in offspring BMI z score in relation to type of diabetes (gestational vs type 1, p = 0.95). CONCLUSIONS/INTERPRETATION: Maternal diabetes is associated with increased offspring BMI z score, although this is no longer apparent after adjustment for maternal pre-pregnancy BMI in the limited number of studies in which this is reported. Causal mediators of the effect of maternal diabetes on offspring outcomes remain to be established; we recommend that future research includes adjustment for maternal pre-pregnancy BMI.

ATP-mediated changes in cross-subunit interactions in the RecA protein.

RecA protein undergoes ATP- and DNA-induced conformational changes that result in different helical parameters for free protein filaments versus RecA/ATP/DNA nucleoprotein filaments. Previous mutational studies of a particular region of the RecA oligomeric interface suggested that cross-subunit contacts made by residues K6 and R28 were more important for stabilization of free protein oligomers than nucleoprotein filaments [Eldin, S., et al. (2000) J. Mol. Biol. 299, 91-101]. Using mutant proteins with specifically engineered Cys substitutions, we show here that the efficiency of cross-subunit disulfide bond formation at certain positions in this region changes in the presence of ATP or ATP/DNA. Our results support the idea that specific cross-subunit interactions that occur within this region of the subunit interface are different in free RecA protein versus RecA/ATP/DNA nucleoprotein filaments.

Phe217 regulates the transfer of allosteric information across the subunit interface of the RecA protein filament.

BACKGROUND: ATP-mediated cooperative assembly of a RecA nucleoprotein filament activates the protein for catalysis of DNA strand exchange. RecA is a classic allosterically regulated enzyme in that ATP binding results in a dramatic increase in ssDNA binding affinity. This increase in ssDNA binding affinity results almost exclusively from an ATP-mediated increase in cooperative filament assembly rather than an increase in the inherent affinity of monomeric RecA for DNA. Therefore, certain residues at the subunit interface must play an important role in transmitting allosteric information across the filament structure of RecA. RESULTS: Using electron microscopic analysis of RecA polymer formation in the absence of DNA, we show that while wild-type RecA undergoes a slight decrease in filament length in the presence of ATP, a Phe217Tyr substitution results in a dramatic ATP-induced increase in cooperative filament assembly. Biosensor DNA binding measurements reveal that the Phe217Tyr mutation increases ATP-mediated cooperative interaction between RecA subunits by more than 250-fold. CONCLUSIONS: These studies represent the first identification of a subunit interface residue in RecA (Phe217) that plays a critical role in regulating the flow of ATP-mediated information throughout the protein filament structure. We propose a model by which conformational changes that occur upon ATP binding are propagated through the structure of a RecA monomer, resulting in the insertion of the Phe217 side chain into a pocket in the neighboring subunit. This event serves as a key step in intersubunit communication leading to ATP-mediated cooperative filament assembly and high affinity binding to ssDNA.

Mutations in the N-terminal region of RecA that disrupt the stability of free protein oligomers but not RecA-DNA complexes.

We have introduced targeted mutations in two areas that make up part of the RecA subunit interface. In the RecA crystal structure, cross-subunit interactions are observed between the Lys6 and Asp139 side-chains, and between the Arg28 and Asn113 side-chains. Unexpectedly, we find that mutations at Lys6 and Arg28 impose sever defects on the oligomeric stability of free RecA protein, whereas mutations at Asn113 or Asp139 do not. However, Lys6 and Arg28 mutant proteins showed an apparent normal formation of RecA-DNA complexes. These results suggest that cross-subunit contacts in this region of the protein are different for free RecA protein filaments versus RecA-DNA nucleoprotein filaments. Mutant proteins with substitutions at either Lys6 or Arg28 show partial inhibition of DNA strand exchange activity, yet the mechanistic reasons for this inhibition appear to be distinct. Although Lys6 and Arg28 appear to be more important to the stability of free RecA protein, as opposed to the stability of the catalytically active nucleoprotein filament, our results support the idea that the cross-subunit interactions made by each residue play an important role in optimizing the catalytic organization of the active RecA oligomer.

Intersubunit proximity of residues in the RecA protein as shown by engineered disulfide cross-links.

Mutational studies of regions that make up the oligomeric interface within the RecA protein filament structure have shown that F217 is an important determinant of RecA function and oligomer stability. All substitutions, other than Tyr and Cys, completely inhibit RecA activities and exhibit a substantial decrease in protein filament stability [Skiba, M. C., and Knight, K. L. (1994) J. Biol. Chem. 269, 3823-3828; Logan, K. M., et al. (1997) J. Mol. Biol. 266, 306-316]. Although the RecA crystal structure exhibits no obvious constraints that explain this mutational stringency, the structure does reveal a hydrophobic pocket in the neighboring monomer that may accommodate the F217 side chain. Together with the F217C mutation, we have introduced a series of Cys substitutions within the interacting surface on the neighboring monomer and have tested for disulfide formation under various conditions, e.g., with or without ATP and ssDNA. We show that the location of F217 in the crystal structure is in general agreement with its position in the catalytically active RecA-ATP-DNA complex. Functional studies with the mutant proteins support the idea that ATP-induced movement of the wild-type F217 side chain toward this hydrophobic pocket is important in mediating allosteric changes in the RecA protein structure.

Mutant RecA proteins which form hexamer-sized oligomers.

We have analyzed the oligomeric properties of a number of mutant RecA proteins containing single amino acid substitutions within one region of the subunit interface. In contrast to wild-type RecA, which forms a heterogeneous population of different-sized oligomers, we find that many of these mutant proteins exist in a more homogeneous oligomeric form, which approximates to the size of a RecA hexamer. Some of these mutants have a significant level of activity in vivo for recombinational DNA repair and thus represent the first mutant RecA proteins identified which retain activity yet can exist in a discrete oligomeric state as free protein.

Mutations at Pro67 in the RecA protein P-loop motif differentially modify coprotease function and separate coprotease from recombination activities.

The functional significance of residues in the RecA protein P-loop motif was assessed by analyzing 100 unique mutants with single amino acid substitutions in this region. Comparison of the effects on the LexA coprotease and recombination activities shows that Pro67 is unique among these residues because only at this position did we find substitutions that caused differential effects on these functions. One mutant, Pro67-->Trp, displays high constitutive coprotease activity and a moderate inhibitory effect on recombination functions. Glu and Asp substitutions result in low level constitutive coprotease activity but dramatically reduce recombination activity. The purified Pro67-->Trp protein shows a completely relaxed specificity for NTP cofactors in LexA cleavage assays and can use shorter length oligonucleotides as cofactors for cleavage of lambda cI repressor than can wild type RecA. Interestingly, both the mutant protein and wild type RecA can use very short oligonucleotides, e.g. (dA)6 and (dT)6, as cofactors for LexA cleavage. We have also found two mutations at position 67, which are completely defective for LexA coprotease activity in vivo but still maintain recombinational DNA repair (Pro67-->Lys) and homologous recombination (Pro67-->Lys and Pro67-->Arg) activities. These findings show that the recombination activities of RecA are mutationally separable from the coprotease function and that Pro67 is located in a functionally important position in the RecA structure.

Functional characterization of residues in the P-loop motif of the RecA protein ATP binding site.

We have introduced a large number of single amino acid substitutions at six positions that lie within the P-loop motif of the ATP binding site in the Escherichia coli RecA protein. The activity of each recA mutant was determined using genetic assays which assess the catalytic proficiency of the RecA protein for both homologous genetic recombination and recombinational repair of damaged DNA. The six residues displayed unique patterns of allowed versus non-allowed substitutions that define the functional and structural constraints at each position. Our results show that while the restricted mutability of Gly66 and Ser70 conform to expectations based on their positions in the RecA crystal structure, strict constraints are in effect at positions 68 and 69 that are not apparent in the RecA structure but would be compatible with the proximity of these side-chains to bound DNA. Thr74 shows a rather unexpected pattern of allowed substitutions that may reflect two distinct structural solutions to optimal stabilization of bound nucleotide. In addition, specific substitutions at Pro67 result in mutant RecA proteins that appear to discriminate between homologous genetic recombination and recombinational DNA repair.

Mutagenesis of the P-loop motif in the ATP binding site of the RecA protein from Escherichia coli.

Using a combinatorial cassette mutagenesis procedure we have introduced a number of mutations into 10 codons that define the P-loop motif within the ATP binding site of the Escherichia coli RecA protein. The recombinational proficiency of the recA mutants was determined using three genetic assays: survival in the presence of 4-nitroquinoline-1-oxide, survival following UV irradiation and the ability to support plaque formation by a red-gam-Chi+ lambda phage. While no amino acid substitutions were allowed at the four residues that define the P-loop consensus sequence, a variety of changes at the other positions in this region were observed that allowed full or partial RecA function. This occurred despite the fact that these residues are very highly conserved among 22 eubacterial RecA proteins, and represent the most conserved stretch of 10 contiguous residues in the entire RecA sequence. Our results show that these residues display marked differences in the ability to support mutations. The mutability of each of these 10 residues is discussed in terms of possible functional and/or structural roles.