1. The principle pathway for transport of lysosomal hydrolases from the trans-Golgi network (pH 6.6) to the late endosomes (pH 6.0) and for recycling of Mannose-6-Phosphate (M6P) receptors back to the Golgi depends on the pH difference between those two compartments. From what you know about M6P-receptor binding and recycling pathways for delivery of material to lysosomes, describe the consequences of changing the pH in those two compartments. a) What would happen if the pH in the late endosomes was raised to pH 6.6? complete the sentence by choosing one for bolded choices. The M6P-receptor would (fail in/ succeed in) releasing its associated cargo and these proteins would be recycled back to the (Smooth ER/Trans-Golgi-compartment/rough ER). As a result, ("proteosomal"/ "endosomal"/ "lysosomal) proteins would fail to be delivered to the ("endosomal/lysosomal/ proteosomal)compartment and would accumulate in the ("TGN/Nucleus/Smooth ER.)

2. The following tyrosine-phosphorylated polypeptides were tested as substrates of protein tyrosine phosphatase, an important enzyme in cellular signal transduction. The pTyr in bold signifies the tyrosine residue that is phosphorylated. The binding affinities of the polypeptide substrates to the enzyme were found to follow the order: (a) > (c) - (d) >> (b). (a) Asp-Ala-Asp-Glu-pTyr-Leu-lle-Pro-Gln-Gln-Gly (b) Pro-Val-Pro-Glu-pTyr-lle-Asn-Ala-Ser-Val (c) Asp-Ala-Glu-Glu-pTyr-Leu-Val-Pro-Gln-Gln-Gly (d) Asp-Asn-Leu-Tyr-pTyr-Trp-Asp-Glu-Asn-Ser-Ser In addition to the presence of the phosphorylated tyrosine residue, what amino acid a) properties of the polypeptides accounts for the relative order of binding affinities to the enzyme? b) the active site of the phosphatase enzyme that are responsible for the affinity of substrate binding? Assume a pH of 7.4 at the enzyme active site. (Note a phosphatase uses phosphate substrate) What amino acids have side chains that would indicate they are…

You are investigating a lysosomal storage disease and you discover that newly synthesized lysosome hydrolases (proteins that should be sent to the lysosome) are secreted from the cells rather than being delivered to the lysosomes (where they should normally be located). What is the most likely explanation for this finding? (Hint:  what might be different about the proteins that would cause them to not end up in the correct location?)

Specificity in fusion between vesicles involves two discrete and sequential processes. Describe the first of the two processes and its regulation by GTPase switch proteins. What effect on the size of early endosomes might result from overexpression of a mutant form of Rab5 that is stuck in the GTP-bound state?