Chronic granulomatous disease (CGD) is a rare inherited immunodeficiency disease that leads to severe recurrent infections. CGD is caused by defects in the phagocyte NADPH oxidase, a multiprotein enzyme that reduces oxygen to superoxide, a precursor of microbicidal oxidants. Less than 6% of CGD patients have an autosomal recessive form of the disease caused by mutations in NCF-2. This gene encodes p67-phox, a cytosolic oxidase subunit that associates with membrane-bound flavocytochrome b558 and regulates electron transfer. We studied six patients from five families with p67-phox deficiency and identified seven different mutant alleles. Patients from three of the kindreds were homozygous for their respective mutation, although the parents of only one family were known to be related. Five of the mutations have not previously been identified: (1) a missense mutation (383C-->T) in exon 5, (2) a nonsense mutation (196C-->T) in exon 3, (3) a missense mutation (230G-->A) in exon 3, (4) a nonsense mutation (298C-->T) in exon 4, and (5) a dinucleotide deletion (835-836 AC) from exon 9. Phagocytes from each of the patients analyzed failed to generate a measurable respiratory burst and had no detectable p67-phox protein. Our results further demonstrate that there is great heterogeneity among the mutations in p67-phox-deficient CGD patients, with no evidence for mutational hot-spots or a founder effect. Our data also support the hypothesis that the stability of p67-phox is particularly sensitive to missense mutations that cause amino acid substitutions within its N-terminal domain. In contrast, mutations predicting single amino acid changes elsewhere in the protein generally represent benign polymorphisms.
X-ray structure of methyl-CpG binding domain (MBD) of MeCP2, an intrinsically disordered protein (IDP) involved in Rett syndrome, offers a rational basis for defining the spatial distribution for most of the sites where mutations responsible of Rett syndrome, RTT, occur. We have ascribed pathogenicity for mutations of amino acids bearing positively charged side chains, all located at the protein-DNA interface, as positive charge removal cause reduction of the MeCP2-DNA adduct lifetime. Pathogenicity of the frequent proline replacements, outside the DNA contact moiety of MBD, can be attributed to the role of this amino acid for maintaining both unfolded states for unbound MeCP2 and, at the same time, to favor some higher conformational order for stabilizing structural determinants required by protein activity. These hypotheses can be extended to transcription repressor domain, TRD, the other MeCP2-DNA interaction site and, in general, to all the IDP that interact with nucleic acids.
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