Disease relevance of MIP

• One other sequenced member of the MIP family (ORF1 of Lactococcus lactis) has no known physiological function [1].
• CONCLUSIONS: This study describes functional expression of MIP in a baculovirus expression system [2].
• After proteolytic digestion of lens fiber membranes with trypsin or Staphylococcus aureus V8 protease the calmodulin-binding activity of MIP is retained [3].
• A native bovine MIP26 amplicon was subcloned into an expression cassette under the control of a constitutive Cauliflower Mosaic Virus promoter, also containing a neomycin phosphotransferase operon [4].

High impact information on MIP

• Synthetic oligonucleotide probes have been used to identify two overlapping cDNA clones that represent the entire coding region of the mRNA for the major intrinsic protein (MIP) of bovine lens cell membrane [5].
• The cDNA hybridizes to the rat genome, but MIP mRNA is not detected in rat liver [5].
• Analysis of the deduced amino acid sequence provides support for the potential role of MIP as a junctional protein [5].
• Differences between liver gap junction protein and lens MIP 26 from rat: implications for tissue specificity of gap junctions [6].
• Soybean nodulin-26, a homologue of bovine eye lens major intrinsic protein (MIP-26), is an integral protein of the peribacteroid membrane in symbiotic root nodules [7].

Biological context of MIP

• CONCLUSIONS: These results represent the first complete MIP sequence map at the amino acid level and identify the single major phosphorylation site at serine 235 [8].
• PURPOSE: To determine the complete primary structure, including posttranslational modifications, of bovine lens major intrinsic protein (MIP) using a recently developed combination of liquid chromatography and mass spectrometry [8].
• RESULTS: The complete sequence of bovine MIP was mapped by molecular weight measurements of CNBr fragments, confirming the reported DNA sequence [8].
• The functions of major intrinsic protein (MIP) of lens are still unresolved; however the sequence homology with channel-forming integral membrane protein (CHIP) and other Aquaporins suggests that MIP is a water channel [9].
• MIP was localized in the nucleus in interphase culture cells as revealed by immunofluorescent light microscopy [10].

Anatomical context of MIP

• Lens membranes, which contain 50-60% of the protein as MIP, were digested with lysylendopeptidase C [11].
• We suggest MIP may behave as an intercellular adhesion protein which can also act as a volume-regulating channel to collapse the lens extracellular space [12].
• These results indicate that MIP consists of two moieties; one domain forms a rigid globule which is essential for its activity to inhibit microtubule assembly, and the other acidic one is highly mobile and tails from the globule [13].
• Thus oocytes expressing MIP failed to exhibit ion channel activity and consistently exhibited water transport by a facilitated pathway that was qualitatively similar to the Aquaporins but of lesser magnitude [9].
• These domains may be responsible for two different functions of MIP, the interaction with the cytoskeleton and the interaction with, for example, nuclear components [13].

Associations of MIP with chemical compounds

• Matrix-assisted laser desorption ionization and electrospray tandem mass spectrometry were employed to obtain molecular weight and sequence data from bovine MIP CNBr fragments, directly or after subsequent digestion with trypsin [8].
• Calf lens fiber plasma membranes, containing only the intrinsic membrane protein MP26 and its maturation product MP22 were treated with proteolytic enzymes such as trypsin, protease V8 from S. aureus or with chemical agents as CNBr in formic acid [14].
• A yeast homologue of the bovine lens fibre MIP gene family complements the growth defect of a Saccharomyces cerevisiae mutant on fermentable sugars but not its defect in glucose-induced RAS-mediated cAMP signalling [15].
• Individual residues in MIP were replaced by residues conserved among the Aquaporins, and introduction of a proline in the 5th transmembrane domain of MIP raised the Pf by 50% [9].
• The major intrinsic protein (MIP) from bovine lens fibre membranes has been purified from unstripped membranes using a single ion-exchange chromatography step (MonoS) in the non-ionic detergent octyl-beta-D-glucopyranoside (OG) [16].

Enzymatic interactions of MIP

• METHODS: The MIP was isolated from bovine lenses by sucrose gradient centrifugation and was cleaved with cyanogen bromide (CNBr) [8].

Other interactions of MIP

• We conclude that MIP functions as an Aquaporin in lens, but the protein may also have other essential functions [9].
• The purpose of this study was to assess the effect of blood contamination on the shear bond strength and failure site of 2 orthodontic primers (Transbond XT and Transbond MIP; 3M/Unitek, Monrovia, Calif) when used with adhesive-precoated brackets (APC II brackets; 3M/Unitek) [17].
• Lateral to the germinative zone were the cells of the transition zone (meridinal rows) where expression of the lens specific proteins beta-crystallin, gamma-crystallin, filensin and aquaporin 0 as well as the lens fiber-, adipocyte- and brain glia-specific Na, K-ATPase catalytic subunit, alpha2 are expressed [18].

Analytical, diagnostic and therapeutic context of MIP

• Separation of the lysylendopeptidase-C-released peptides on C8 reversed-phase HPLC demonstrated that one of these fragments, corresponding to residues 239-259 in MIP, was partially phosphorylated [11].
• Sequence analysis of peptide fragments from the intrinsic membrane protein of calf lens fibers MP26 and its natural maturation product MP22 [14].
• Immunocytochemical localization of the main intrinsic polypeptide (MIP) in ultrathin frozen sections of rat lens [19].
• Thus, the structure of thin and wavy junctions differed only in the extent of crystallization of MIP, a property that can explain why this protein can produce two different antibody-labeling patterns [12].
• Characterisation of the major intrinsic protein (MIP) from bovine lens fibre membranes by electron microscopy and hydrodynamics [16].

References