Fig. 3

Proteins immunoprecipitating with Sgcg. Total normalized spectral counts were determined by adding counts from triplicate biological replicates of co-IPs from Rx or RIPA extracts, weighted for differences in protein mass. Increases in protein abundance were identified by ANOVA (green arrows), as compared with samples with statistically fewer spectral counts (red arrows); arrow order corresponds to the columns of total normalized weighted spectral counts. Candidate direct or indirect interactors, selected as described in “Methods,” were ranked in order of increasing P value. A Only protein phosphatase 1B, catalytic subunit (PP1β)) was significant in Rx buffer. B Top Candidate Interactors from RIPA1-solubilized membranes were defined as those recovered with anti-Sgcg antibody from both muscle genotypes containing Sgcg (WT, Svil^−/−) and represented by fewer than half as many total normalized weighted spectral counts in each of the two sets of control IPs. One control was IPs with anti-Sgcg antibody from Sgcg^−/− muscles; the second was IPs with a nonspecific rabbit IgG (Rb IgG) from muscle of any genotype. Other Candidate Interactors with P values < 0.05 either exhibited higher than expected background counts or were significantly enriched only in Svil^−/− muscles. Values for sarcoglycans not flagged as statistically significant are shown in italics for comparison with the newly identified candidate Sgcg interactors. The candidate interactors MYPT2 and NKCC1 also are italicized because the numbers of counts in Sgcg^−/− muscle just miss the arbitrary 50% threshold. Other Candidate Interactors fell into two categories. Myotilin and titin met the Sgcg^−/− muscle cut-off criterion if the average of the backgrounds observed with control IgG were first subtracted from total normalized counts. Tensin 2, PUR6, and palladin met criteria only for Svil^−/− muscle